/* ==========================================================================
   WebLab STEM - Design System & Modern UI Stylesheet
   Chuẩn UI Hiện đại: Glassmorphism, Micro-animations, Dark/Light Mode
   ========================================================================== */

:root {
  /* Color Palette - Cyber STEM Theme */
  --bg-primary: #0a0f1d;
  --bg-secondary: #111827;
  --bg-tertiary: #1f293d;
  --bg-glass: rgba(17, 24, 39, 0.75);
  --bg-glass-card: rgba(31, 41, 61, 0.55);
  --border-glass: rgba(255, 255, 255, 0.08);
  --border-hover: rgba(56, 189, 248, 0.4);

  --text-primary: #f8fafc;
  --text-secondary: #94a3b8;
  --text-muted: #7c8da5;

  /* Accent Colors for Subjects */
  --physics-accent: #38bdf8;       /* Electric Cyan */
  --physics-glow: rgba(56, 189, 248, 0.25);
  --chemistry-accent: #f43f5e;     /* Quantum Rose */
  --chemistry-glow: rgba(244, 63, 94, 0.25);
  --math-accent: #a855f7;          /* Matrix Purple */
  --math-glow: rgba(168, 85, 247, 0.25);
  --biology-accent: #10b981;       /* Bio Emerald */
  --biology-glow: rgba(16, 185, 129, 0.25);

  --brand-gradient: linear-gradient(135deg, #38bdf8 0%, #818cf8 50%, #c084fc 100%);
  --brand-glow: 0 0 25px rgba(56, 189, 248, 0.35);

  --radius-sm: 8px;
  --radius-md: 14px;
  --radius-lg: 20px;
  --radius-full: 9999px;

  --shadow-sm: 0 2px 8px rgba(0, 0, 0, 0.2);
  --shadow-md: 0 10px 30px rgba(0, 0, 0, 0.35);
  --shadow-lg: 0 20px 50px rgba(0, 0, 0, 0.5);

  --font-sans: 'Inter', system-ui, -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, sans-serif;
  --font-mono: 'JetBrains Mono', 'Fira Code', Consolas, monospace;

  --transition-fast: 0.2s cubic-bezier(0.4, 0, 0.2, 1);
  --transition-normal: 0.3s cubic-bezier(0.4, 0, 0.2, 1);
  --transition-slow: 0.5s cubic-bezier(0.4, 0, 0.2, 1);
}

/* Skip layout and paint work for content far below the viewport. */
.mission-section,
.lookup-portal-section,
.subjects-hub-section,
.seo-knowledge-section,
.subject-purpose-section,
.learning-center-section,
.author-section,
footer {
  content-visibility: auto;
  contain-intrinsic-size: auto 900px;
}

/* ========================================================================== 
   Personalized Learning Center
   ========================================================================== */
.learning-center-section {
  position: relative;
  padding: 4.5rem 0;
  background:
    radial-gradient(circle at 12% 0%, rgba(16, 185, 129, 0.13), transparent 34%),
    radial-gradient(circle at 88% 100%, rgba(56, 189, 248, 0.12), transparent 34%),
    var(--bg-secondary);
  border-top: 1px solid var(--border-glass);
  border-bottom: 1px solid var(--border-glass);
}

.learning-center-header {
  align-items: flex-end;
  gap: 1.5rem;
}

.learning-center-tag {
  color: #34d399;
  background: rgba(16, 185, 129, 0.14);
}

.learning-center-intro {
  max-width: 780px;
  margin-top: 0.75rem;
  color: var(--text-secondary);
}

.learning-privacy-note {
  display: inline-flex;
  align-items: center;
  gap: 0.55rem;
  max-width: 330px;
  padding: 0.7rem 0.9rem;
  color: var(--text-secondary);
  background: rgba(16, 185, 129, 0.08);
  border: 1px solid rgba(16, 185, 129, 0.25);
  border-radius: var(--radius-md);
  font-size: 0.82rem;
  line-height: 1.45;
}

.learning-privacy-note i {
  color: #34d399;
}

.learning-center-app {
  display: grid;
  gap: 1.25rem;
}

.sr-only {
  position: absolute !important;
  width: 1px !important;
  height: 1px !important;
  padding: 0 !important;
  margin: -1px !important;
  overflow: hidden !important;
  clip: rect(0, 0, 0, 0) !important;
  white-space: nowrap !important;
  border: 0 !important;
}

.learning-profile-card,
.learning-dashboard,
.learning-workspace,
.learning-empty-state {
  background: var(--bg-glass-card);
  border: 1px solid var(--border-glass);
  border-radius: var(--radius-lg);
  box-shadow: var(--shadow-sm);
}

.learning-profile-card {
  display: grid;
  grid-template-columns: minmax(0, 1fr) auto;
  gap: 1rem;
  padding: 1.1rem;
}

.learning-profile-fields {
  display: grid;
  grid-template-columns: repeat(3, minmax(0, 1fr));
  gap: 0.8rem;
}

.learning-field {
  display: grid;
  gap: 0.38rem;
}

.learning-field label,
.learning-field-label {
  color: var(--text-secondary);
  font-size: 0.78rem;
  font-weight: 700;
}

.learning-field select,
.learning-field input,
.learning-field textarea,
.learning-notebook textarea,
.learning-notebook input {
  width: 100%;
  padding: 0.72rem 0.8rem;
  color: var(--text-primary);
  background: var(--bg-primary);
  border: 1px solid var(--border-glass);
  border-radius: var(--radius-sm);
  transition: border-color var(--transition-fast), box-shadow var(--transition-fast);
}

.learning-field textarea,
.learning-notebook textarea {
  min-height: 92px;
  resize: vertical;
  line-height: 1.5;
}

.learning-field select:focus-visible,
.learning-field input:focus-visible,
.learning-field textarea:focus-visible,
.learning-notebook textarea:focus-visible,
.learning-notebook input:focus-visible,
.learning-center-app button:focus-visible,
.learning-center-app a:focus-visible {
  outline: 3px solid rgba(56, 189, 248, 0.35);
  outline-offset: 2px;
  border-color: var(--physics-accent);
}

.learning-profile-actions {
  display: flex;
  align-items: end;
  gap: 0.6rem;
}

.learning-btn {
  min-height: 44px;
  display: inline-flex;
  align-items: center;
  justify-content: center;
  gap: 0.45rem;
  padding: 0.68rem 1rem;
  color: var(--text-primary);
  background: var(--bg-tertiary);
  border: 1px solid var(--border-glass);
  border-radius: var(--radius-sm);
  cursor: pointer;
  font-weight: 750;
  transition: transform var(--transition-fast), border-color var(--transition-fast), background var(--transition-fast);
}

.learning-btn:hover {
  border-color: var(--border-hover);
  transform: translateY(-1px);
}

.learning-btn-primary {
  color: #03131d;
  background: linear-gradient(135deg, #38bdf8, #34d399);
  border-color: transparent;
}

.learning-btn-danger {
  color: #fda4af;
  border-color: rgba(244, 63, 94, 0.35);
}

.learning-btn[disabled] {
  cursor: not-allowed;
  opacity: 0.5;
  transform: none;
}

.learning-dashboard {
  display: grid;
  grid-template-columns: 180px minmax(0, 1fr) minmax(240px, 0.7fr);
  gap: 1rem;
  padding: 1rem;
}

.learning-progress-summary {
  display: grid;
  place-items: center;
  padding: 0.9rem;
  text-align: center;
  background: rgba(56, 189, 248, 0.06);
  border: 1px solid rgba(56, 189, 248, 0.2);
  border-radius: var(--radius-md);
}

.learning-progress-ring {
  --progress: 0;
  width: 92px;
  height: 92px;
  display: grid;
  place-items: center;
  border-radius: 50%;
  background: conic-gradient(#34d399 calc(var(--progress) * 1%), rgba(148, 163, 184, 0.18) 0);
  position: relative;
}

.learning-progress-ring::before {
  content: '';
  position: absolute;
  inset: 8px;
  border-radius: 50%;
  background: var(--bg-secondary);
}

.learning-progress-ring strong {
  position: relative;
  z-index: 1;
  font-size: 1.25rem;
}

.learning-progress-summary p {
  margin-top: 0.55rem;
  color: var(--text-secondary);
  font-size: 0.78rem;
}

.learning-dashboard-block {
  min-width: 0;
  padding: 0.85rem;
  background: rgba(148, 163, 184, 0.04);
  border: 1px solid var(--border-glass);
  border-radius: var(--radius-md);
}

.learning-dashboard-block h3 {
  margin-bottom: 0.55rem;
  font-size: 0.95rem;
}

.learning-mastery-block {
  grid-column: 1 / -1;
}

.learning-mastery-heading,
.learning-mastery-summary {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 0.75rem;
}

.learning-mastery-summary {
  flex-wrap: wrap;
  justify-content: flex-end;
  color: var(--text-secondary);
  font-size: 0.75rem;
}

.learning-mastery-summary span {
  padding: 0.25rem 0.5rem;
  background: rgba(148, 163, 184, 0.08);
  border-radius: var(--radius-full);
}

.learning-mastery-grid {
  display: grid;
  grid-template-columns: repeat(2, minmax(0, 1fr));
  gap: 0.55rem 1rem;
}

.learning-mastery-row {
  display: grid;
  grid-template-columns: minmax(80px, 0.35fr) minmax(100px, 1fr) 42px;
  align-items: center;
  gap: 0.55rem;
  color: var(--text-secondary);
  font-size: 0.75rem;
}

.learning-mastery-row > div {
  height: 7px;
  overflow: hidden;
  background: rgba(148, 163, 184, 0.15);
  border-radius: var(--radius-full);
}

.learning-mastery-row > div i {
  display: block;
  height: 100%;
  background: var(--mastery-accent, #38bdf8);
  border-radius: inherit;
}

.learning-mastery-row strong {
  color: var(--text-primary);
  text-align: right;
}

.learning-recommendation {
  display: grid;
  gap: 0.45rem;
  color: var(--text-secondary);
  font-size: 0.86rem;
}

.learning-recommendation strong {
  color: var(--text-primary);
}

.learning-error-list {
  display: flex;
  flex-wrap: wrap;
  gap: 0.4rem;
}

.learning-error-chip,
.learning-status-chip,
.learning-meta-chip {
  display: inline-flex;
  align-items: center;
  gap: 0.32rem;
  padding: 0.28rem 0.52rem;
  border-radius: var(--radius-full);
  font-size: 0.72rem;
  font-weight: 750;
}

.learning-error-chip {
  color: #fdba74;
  background: rgba(249, 115, 22, 0.12);
  border: 1px solid rgba(249, 115, 22, 0.25);
}

.learning-topic-section {
  display: grid;
  gap: 0.75rem;
}

.learning-topic-section-header {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 1rem;
}

.learning-topic-section-header p {
  color: var(--text-secondary);
  font-size: 0.85rem;
}

.learning-topic-tools {
  display: flex;
  align-items: center;
  gap: 0.45rem;
  width: min(100%, 430px);
}

.learning-topic-search {
  min-height: 46px;
  display: flex;
  flex: 1;
  align-items: center;
  gap: 0.6rem;
  padding: 0 0.85rem;
  color: var(--text-muted);
  background: color-mix(in srgb, var(--bg-primary) 82%, transparent);
  border: 1px solid var(--border-glass);
  border-radius: var(--radius-sm);
  transition: border-color var(--transition-fast), box-shadow var(--transition-fast);
}

.learning-topic-search:focus-within {
  color: var(--physics-accent);
  border-color: var(--physics-accent);
  box-shadow: 0 0 0 3px rgba(56, 189, 248, 0.1);
}

.learning-topic-search input {
  min-width: 0;
  width: 100%;
  min-height: 44px;
  color: var(--text-primary);
  background: transparent;
}

.learning-topic-search input::placeholder {
  color: var(--text-muted);
}

.learning-clear-search {
  flex: 0 0 46px;
  width: 46px;
  padding: 0;
}

.learning-topic-grid {
  display: grid;
  grid-template-columns: repeat(4, minmax(0, 1fr));
  gap: 0.8rem;
}

.learning-topic-card {
  min-width: 0;
  display: flex;
  flex-direction: column;
  gap: 0.65rem;
  padding: 1rem;
  background: var(--bg-glass-card);
  border: 1px solid var(--border-glass);
  border-radius: var(--radius-md);
  transition: transform var(--transition-fast), border-color var(--transition-fast);
}

.learning-topic-card:hover,
.learning-topic-card.is-active {
  transform: translateY(-2px);
  border-color: var(--topic-accent, var(--physics-accent));
}

.learning-topic-card h3 {
  font-size: 0.98rem;
  line-height: 1.35;
}

.learning-topic-card p {
  flex: 1;
  color: var(--text-secondary);
  font-size: 0.8rem;
  line-height: 1.5;
}

.learning-topic-card-top,
.learning-topic-meta {
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  justify-content: space-between;
  gap: 0.45rem;
}

.learning-subject-icon {
  width: 34px;
  height: 34px;
  display: inline-grid;
  place-items: center;
  color: var(--topic-accent, var(--physics-accent));
  background: rgba(56, 189, 248, 0.1);
  background: color-mix(in srgb, var(--topic-accent, var(--physics-accent)) 12%, transparent);
  border-radius: 10px;
}

.learning-status-chip {
  color: var(--text-secondary);
  background: rgba(148, 163, 184, 0.1);
}

.learning-status-chip.is-complete {
  color: #6ee7b7;
  background: rgba(16, 185, 129, 0.12);
}

.learning-status-chip.needs-review {
  color: #fdba74;
  background: rgba(249, 115, 22, 0.12);
}

.learning-meta-chip {
  color: var(--text-secondary);
  background: rgba(148, 163, 184, 0.07);
}

.learning-meta-chip.is-foundation-ready {
  color: #6ee7b7;
  background: rgba(16, 185, 129, 0.1);
}

.learning-meta-chip.needs-foundation {
  color: #fde68a;
  background: rgba(245, 158, 11, 0.1);
}

.learning-workspace {
  overflow: hidden;
}

.learning-workspace-header {
  display: flex;
  align-items: flex-start;
  justify-content: space-between;
  gap: 1rem;
  padding: 1.1rem 1.2rem;
  background: linear-gradient(135deg, rgba(56, 189, 248, 0.1), rgba(16, 185, 129, 0.07));
  border-bottom: 1px solid var(--border-glass);
}

.learning-workspace-header h3 {
  margin-bottom: 0.25rem;
  font-size: 1.15rem;
}

.learning-workspace-header p {
  color: var(--text-secondary);
  font-size: 0.84rem;
}

.learning-readiness {
  display: grid;
  gap: 0.65rem;
  padding: 0.85rem 1.2rem 0.95rem;
  background: rgba(15, 23, 42, 0.24);
  border-bottom: 1px solid var(--border-glass);
}

[data-theme="light"] .learning-readiness {
  background: rgba(241, 245, 249, 0.78);
}

.learning-readiness-heading {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 0.75rem;
  font-size: 0.78rem;
}

.learning-readiness-heading strong {
  display: inline-flex;
  align-items: center;
  gap: 0.45rem;
}

.learning-readiness-heading strong i {
  color: var(--physics-accent);
}

.learning-readiness-heading span {
  color: var(--text-secondary);
}

.learning-readiness-bar {
  height: 6px;
  overflow: hidden;
  background: rgba(148, 163, 184, 0.16);
  border-radius: var(--radius-full);
}

.learning-readiness-bar span {
  display: block;
  height: 100%;
  background: linear-gradient(90deg, #38bdf8, #34d399);
  border-radius: inherit;
  transition: width var(--transition-normal);
}

.learning-readiness ul {
  display: flex;
  flex-wrap: wrap;
  gap: 0.45rem;
  list-style: none;
}

.learning-readiness li {
  display: inline-flex;
  align-items: center;
  gap: 0.35rem;
  padding: 0.3rem 0.55rem;
  color: var(--text-muted);
  background: rgba(148, 163, 184, 0.07);
  border: 1px solid var(--border-glass);
  border-radius: var(--radius-full);
  font-size: 0.72rem;
  font-weight: 700;
}

.learning-readiness li.is-done {
  color: #6ee7b7;
  background: rgba(16, 185, 129, 0.1);
  border-color: rgba(16, 185, 129, 0.24);
}

[data-theme="light"] .learning-readiness li.is-done {
  color: #047857;
}

.learning-stepper {
  display: grid;
  grid-template-columns: repeat(7, minmax(0, 1fr));
  border-bottom: 1px solid var(--border-glass);
  overflow-x: auto;
}

.learning-step-btn {
  min-width: 112px;
  min-height: 62px;
  padding: 0.6rem 0.45rem;
  color: var(--text-secondary);
  background: transparent;
  border-right: 1px solid var(--border-glass);
  cursor: pointer;
  font-size: 0.73rem;
  font-weight: 750;
}

.learning-step-btn span {
  width: 24px;
  height: 24px;
  display: inline-grid;
  place-items: center;
  margin-right: 0.3rem;
  color: var(--text-primary);
  background: var(--bg-tertiary);
  border-radius: 50%;
}

.learning-step-btn.is-active {
  color: #7dd3fc;
  background: rgba(56, 189, 248, 0.1);
  box-shadow: inset 0 -3px #38bdf8;
}

.learning-step-btn.is-visited span {
  color: #052e24;
  background: #34d399;
}

.learning-step-content {
  display: grid;
  grid-template-columns: minmax(0, 1.35fr) minmax(300px, 0.65fr);
  gap: 1rem;
  padding: 1.2rem;
}

.learning-panel,
.learning-notebook {
  min-width: 0;
  padding: 1rem;
  background: rgba(15, 23, 42, 0.18);
  border: 1px solid var(--border-glass);
  border-radius: var(--radius-md);
}

[data-theme="light"] .learning-panel,
[data-theme="light"] .learning-notebook {
  background: rgba(248, 250, 252, 0.7);
}

.learning-panel h4,
.learning-notebook h4 {
  margin-bottom: 0.7rem;
  font-size: 1rem;
}

.learning-panel h5 {
  margin: 1rem 0 0.45rem;
  font-size: 0.86rem;
}

.learning-objective-list,
.learning-concept-list,
.learning-procedure-list,
.learning-safety-list {
  display: grid;
  gap: 0.5rem;
  margin-left: 1.15rem;
  color: var(--text-secondary);
  font-size: 0.86rem;
}

.learning-foundation-list,
.learning-reference-list {
  display: grid;
  gap: 0.5rem;
  list-style: none;
}

.learning-foundation-list li {
  display: grid;
  grid-template-columns: 18px minmax(0, 1fr) auto;
  align-items: center;
  gap: 0.5rem;
  padding: 0.55rem 0.65rem;
  color: #fbbf24;
  background: rgba(245, 158, 11, 0.07);
  border: 1px solid rgba(245, 158, 11, 0.18);
  border-radius: var(--radius-sm);
  font-size: 0.78rem;
}

.learning-foundation-list li.is-ready {
  color: #6ee7b7;
  background: rgba(16, 185, 129, 0.07);
  border-color: rgba(16, 185, 129, 0.18);
}

.learning-foundation-list button {
  min-height: 44px;
  padding: 0;
  color: var(--text-primary);
  text-align: left;
  background: transparent;
  border: 0;
  cursor: pointer;
  font-weight: 750;
}

.learning-foundation-list span {
  color: currentColor;
  font-size: 0.7rem;
}

.learning-reference-list li {
  display: flex;
  align-items: flex-start;
  gap: 0.5rem;
  color: var(--text-secondary);
  font-size: 0.8rem;
}

.learning-reference-list i {
  margin-top: 0.18rem;
  color: #34d399;
}

.learning-reference-list a {
  color: #7dd3fc;
  text-decoration: underline;
  text-decoration-color: rgba(125, 211, 252, 0.35);
  text-underline-offset: 3px;
}

.learning-concept-card {
  margin-bottom: 0.65rem;
  padding: 0.8rem;
  background: rgba(56, 189, 248, 0.06);
  border-left: 3px solid #38bdf8;
  border-radius: 0 var(--radius-sm) var(--radius-sm) 0;
}

.learning-concept-card strong {
  display: block;
  margin-bottom: 0.25rem;
}

.learning-concept-card p {
  color: var(--text-secondary);
  font-size: 0.84rem;
}

.learning-content-meta {
  display: flex;
  flex-wrap: wrap;
  gap: 0.45rem;
  margin-bottom: 0.65rem;
}

.learning-content-meta span {
  display: inline-flex;
  align-items: center;
  gap: 0.35rem;
  padding: 0.3rem 0.55rem;
  color: var(--text-secondary);
  background: rgba(148, 163, 184, 0.07);
  border: 1px solid var(--border-glass);
  border-radius: var(--radius-full);
  font-size: 0.72rem;
  font-weight: 700;
}

.learning-content-meta i,
.learning-quality-note i {
  color: #34d399;
}

.learning-quality-note {
  display: flex;
  align-items: flex-start;
  gap: 0.5rem;
  margin-bottom: 0.75rem;
  color: var(--text-secondary);
  font-size: 0.8rem;
  line-height: 1.5;
}

.learning-question {
  margin-bottom: 0.9rem;
  padding: 0.85rem;
  background: rgba(148, 163, 184, 0.05);
  border: 1px solid var(--border-glass);
  border-radius: var(--radius-sm);
}

.learning-question legend {
  width: 100%;
  margin-bottom: 0.55rem;
  color: var(--text-primary);
  font-size: 0.86rem;
  font-weight: 750;
}

.learning-choice {
  display: flex;
  align-items: flex-start;
  gap: 0.55rem;
  min-height: 42px;
  padding: 0.5rem 0.6rem;
  color: var(--text-secondary);
  border-radius: 7px;
  cursor: pointer;
}

.learning-choice:hover {
  background: rgba(56, 189, 248, 0.07);
}

.learning-choice.is-answer {
  color: #a7f3d0;
  background: rgba(16, 185, 129, 0.08);
  outline: 1px solid rgba(16, 185, 129, 0.22);
}

[data-theme="light"] .learning-choice.is-answer {
  color: #047857;
}

.learning-choice input {
  width: 18px;
  height: 18px;
  margin-top: 0.12rem;
  accent-color: #38bdf8;
}

.learning-question-feedback,
.learning-result-box,
.learning-guidance-box {
  margin-top: 0.65rem;
  padding: 0.7rem 0.8rem;
  border-radius: var(--radius-sm);
  color: var(--text-secondary);
  font-size: 0.82rem;
}

.learning-question-feedback.is-correct,
.learning-result-box.is-good {
  color: #a7f3d0;
  background: rgba(16, 185, 129, 0.1);
  border: 1px solid rgba(16, 185, 129, 0.25);
}

.learning-question-feedback.is-wrong,
.learning-result-box.needs-review {
  color: #fed7aa;
  background: rgba(249, 115, 22, 0.1);
  border: 1px solid rgba(249, 115, 22, 0.25);
}

.learning-question-feedback > strong:first-child {
  display: inline-flex;
  align-items: center;
  gap: 0.3rem;
}

.learning-correct-answer,
.learning-result-guidance {
  display: block;
  margin-top: 0.45rem;
}

.learning-correct-answer {
  padding-top: 0.45rem;
  color: var(--text-primary);
  border-top: 1px solid rgba(249, 115, 22, 0.2);
}

.learning-targeted-review {
  display: grid;
  gap: 0.55rem;
  margin: 0.65rem 0;
  padding: 0.75rem 0.8rem;
  color: var(--text-secondary);
  background: rgba(245, 158, 11, 0.07);
  border: 1px solid rgba(245, 158, 11, 0.2);
  border-radius: var(--radius-sm);
  font-size: 0.8rem;
}

.learning-targeted-review > strong {
  display: inline-flex;
  align-items: center;
  gap: 0.4rem;
  color: #fde68a;
}

.learning-targeted-review ul {
  display: grid;
  gap: 0.4rem;
  margin-left: 1rem;
}

.learning-targeted-review li span {
  margin-right: 0.35rem;
  color: var(--text-primary);
  font-weight: 750;
}

.learning-guidance-box {
  background: rgba(168, 85, 247, 0.08);
  border: 1px solid rgba(168, 85, 247, 0.22);
}

.learning-panel-actions,
.learning-notebook-actions {
  display: flex;
  flex-wrap: wrap;
  gap: 0.6rem;
  margin-top: 0.9rem;
}

.learning-notebook {
  display: grid;
  align-content: start;
  gap: 0.7rem;
}

.learning-notebook-header {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 0.6rem;
  min-height: 44px;
  cursor: pointer;
  list-style: none;
}

.learning-notebook-header::-webkit-details-marker {
  display: none;
}

.learning-notebook-header::after {
  content: '\f078';
  margin-left: auto;
  color: var(--text-muted);
  font-family: 'Font Awesome 6 Free';
  font-weight: 900;
  transition: transform var(--transition-fast);
}

.learning-notebook[open] > .learning-notebook-header::after {
  transform: rotate(180deg);
}

.learning-notebook-body {
  display: grid;
  gap: 0.7rem;
}

.learning-autosave {
  color: #6ee7b7;
  font-size: 0.72rem;
}

.learning-empty-state {
  padding: 2rem;
  text-align: center;
  color: var(--text-secondary);
}

.learning-empty-state i {
  display: block;
  margin-bottom: 0.7rem;
  color: var(--text-muted);
  font-size: 2rem;
}

@media (max-width: 1100px) {
  .learning-topic-grid {
    grid-template-columns: repeat(2, minmax(0, 1fr));
  }

  .learning-dashboard {
    grid-template-columns: 150px minmax(0, 1fr);
  }

  .learning-dashboard-block:last-child {
    grid-column: 1 / -1;
  }
}

@media (max-width: 800px) {
  .learning-center-section {
    padding: 3rem 0;
  }

  .learning-center-header,
  .learning-profile-card,
  .learning-workspace-header {
    align-items: stretch;
    flex-direction: column;
  }

  .learning-profile-card {
    grid-template-columns: 1fr;
  }

  .learning-profile-fields,
  .learning-dashboard,
  .learning-step-content {
    grid-template-columns: 1fr;
  }

  .learning-mastery-grid {
    grid-template-columns: 1fr;
  }

  .learning-mastery-heading {
    align-items: flex-start;
    flex-direction: column;
  }

  .learning-mastery-summary {
    justify-content: flex-start;
  }

  .learning-step-content {
    padding: 0.9rem;
  }

  .learning-stepper {
    position: sticky;
    top: 58px;
    z-index: 8;
    display: flex;
    overflow-x: auto;
    overscroll-behavior-inline: contain;
    scroll-snap-type: x proximity;
    scrollbar-width: thin;
    background: color-mix(in srgb, var(--bg-secondary) 94%, transparent);
    backdrop-filter: blur(14px);
    -webkit-overflow-scrolling: touch;
  }

  .learning-step-btn {
    flex: 0 0 108px;
    min-height: 58px;
    scroll-snap-align: start;
  }

  .learning-notebook {
    order: -1;
  }

  .learning-notebook:not([open]) {
    padding-block: 0.5rem;
  }

  .learning-choice {
    min-height: 48px;
    padding: 0.68rem;
  }

  .learning-profile-actions {
    align-items: stretch;
  }

  .learning-dashboard-block:last-child {
    grid-column: auto;
  }
}

@media (max-width: 560px) {
  .learning-center-section .section-container {
    padding-inline: 0.85rem;
  }

  .learning-topic-grid {
    grid-template-columns: 1fr;
  }

  .learning-profile-card,
  .learning-dashboard,
  .learning-workspace-header,
  .learning-step-content {
    padding: 0.8rem;
  }

  .learning-panel,
  .learning-notebook,
  .learning-topic-card {
    padding: 0.85rem;
  }

  .learning-workspace-header .learning-btn {
    width: 100%;
  }

  .learning-foundation-list li {
    grid-template-columns: 18px minmax(0, 1fr);
  }

  .learning-foundation-list span {
    grid-column: 2;
  }

  .learning-profile-fields,
  .learning-profile-actions,
  .learning-panel-actions,
  .learning-notebook-actions {
    grid-template-columns: 1fr;
  }

  .learning-profile-actions,
  .learning-panel-actions,
  .learning-notebook-actions {
    display: grid;
  }

  .learning-panel-actions {
    position: sticky;
    bottom: 0;
    z-index: 5;
    margin-inline: -0.4rem;
    padding: 0.65rem 0.4rem calc(0.65rem + env(safe-area-inset-bottom));
    background: color-mix(in srgb, var(--bg-secondary) 94%, transparent);
    backdrop-filter: blur(12px);
  }

  .learning-btn,
  .learning-field select,
  .learning-field input,
  .learning-notebook input {
    min-height: 48px;
  }
}

@media (hover: none) {
  .learning-btn:hover,
  .learning-topic-card:hover {
    transform: none;
  }
}

@media (prefers-reduced-motion: reduce) {
  .learning-center-app *,
  .learning-center-app *::before,
  .learning-center-app *::after {
    scroll-behavior: auto !important;
    animation-duration: 0.01ms !important;
    transition-duration: 0.01ms !important;
  }
}

[data-theme="light"] {
  --bg-primary: #f8fafc;
  --bg-secondary: #ffffff;
  --bg-tertiary: #f1f5f9;
  --bg-glass: rgba(255, 255, 255, 0.85);
  --bg-glass-card: rgba(255, 255, 255, 0.7);
  --border-glass: rgba(0, 0, 0, 0.08);
  --border-hover: rgba(14, 165, 233, 0.5);

  --text-primary: #0f172a;
  --text-secondary: #475569;
  --text-muted: #64748b;

  --shadow-sm: 0 2px 8px rgba(0, 0, 0, 0.05);
  --shadow-md: 0 10px 25px rgba(0, 0, 0, 0.08);
  --shadow-lg: 0 20px 40px rgba(0, 0, 0, 0.12);
}

/* ==========================================================================
   Reset & Base Styles
   ========================================================================== */
*, *::before, *::after {
  box-sizing: border-box;
  margin: 0;
  padding: 0;
}

html {
  scroll-behavior: smooth;
  font-family: var(--font-sans);
  background-color: var(--bg-primary);
  color: var(--text-primary);
  line-height: 1.6;
}

body {
  min-height: 100vh;
  display: flex;
  flex-direction: column;
  overflow-x: hidden;
  background-image: 
    radial-gradient(at 0% 0%, rgba(56, 189, 248, 0.08) 0px, transparent 50%),
    radial-gradient(at 100% 100%, rgba(168, 85, 247, 0.08) 0px, transparent 50%);
  background-attachment: fixed;
}

a {
  color: inherit;
  text-decoration: none;
  transition: color var(--transition-fast);
}

button, input, select, textarea {
  font-family: inherit;
  color: inherit;
  outline: none;
  border: none;
}

:where(a, button, input, select, textarea, summary):focus-visible {
  outline: 3px solid color-mix(in srgb, var(--physics-accent) 48%, transparent);
  outline-offset: 3px;
}

:where(section[id], article[id]) {
  scroll-margin-top: 76px;
}

/* ==========================================================================
   Navigation Bar
   ========================================================================== */
.navbar {
  position: sticky;
  top: 0;
  z-index: 100;
  backdrop-filter: blur(16px);
  -webkit-backdrop-filter: blur(16px);
  background-color: var(--bg-glass);
  border-bottom: 1px solid var(--border-glass);
  transition: background-color var(--transition-normal);
}

.nav-container {
  max-width: 1400px;
  margin: 0 auto;
  padding: 0.65rem 1.25rem;
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 0.85rem;
  width: 100%;
  box-sizing: border-box;
}

.brand-logo {
  display: flex;
  align-items: center;
  gap: 0.65rem;
  font-size: 1.25rem;
  font-weight: 800;
  letter-spacing: -0.02em;
  text-decoration: none;
  flex-shrink: 0;
}

.brand-icon {
  width: 36px;
  height: 36px;
  border-radius: var(--radius-sm);
  background: var(--brand-gradient);
  display: flex;
  align-items: center;
  justify-content: center;
  color: #fff;
  font-size: 1.15rem;
  box-shadow: var(--brand-glow);
  flex-shrink: 0;
}

.brand-name span {
  background: var(--brand-gradient);
  -webkit-background-clip: text;
  -webkit-text-fill-color: transparent;
}

.nav-back-pill {
  white-space: nowrap !important;
  display: inline-flex !important;
  align-items: center;
  gap: 0.35rem;
  font-size: 0.78rem;
  font-weight: 700;
  padding: 0.35rem 0.75rem;
  border-radius: 999px;
  text-decoration: none;
  background: rgba(255, 255, 255, 0.08);
  border: 1px solid var(--border-glass);
  color: var(--text-primary);
  transition: all var(--transition-fast);
  flex-shrink: 0;
}

.nav-back-pill:hover {
  background: rgba(56, 189, 248, 0.15);
  border-color: var(--physics-accent);
  color: var(--physics-accent);
  transform: translateX(-2px);
}

.nav-links {
  display: flex;
  align-items: center;
  list-style: none;
  gap: 0.5rem;
  margin: 0;
  padding: 0;
  flex-wrap: nowrap;
}

.nav-item a {
  font-size: 0.88rem;
  font-weight: 600;
  color: var(--text-secondary);
  padding: 0.4rem 0.65rem;
  border-radius: var(--radius-sm);
  display: flex;
  align-items: center;
  gap: 0.35rem;
  transition: all var(--transition-fast);
  text-decoration: none;
  white-space: nowrap;
}

.nav-item a:hover,
.nav-item.active a {
  color: var(--text-primary);
  background-color: rgba(255, 255, 255, 0.08);
}

.nav-badge-physics { color: var(--physics-accent) !important; }
.nav-badge-chem { color: var(--chemistry-accent) !important; }
.nav-badge-math { color: var(--math-accent) !important; }
.nav-badge-bio { color: var(--biology-accent) !important; }

.nav-actions {
  display: flex;
  align-items: center;
  gap: 0.5rem;
  flex-shrink: 0;
}

.mobile-menu-toggle {
  width: 44px;
  height: 44px;
  display: none;
  place-items: center;
  flex: 0 0 44px;
  color: var(--text-primary);
  background: var(--bg-glass-card);
  border: 1px solid var(--border-glass);
  border-radius: var(--radius-sm);
  cursor: pointer;
}

/* Direct Language Pill Buttons (Compact EN & VI) */
.lang-switch-group {
  display: inline-flex;
  align-items: center;
  background-color: var(--bg-glass-card);
  border: 1px solid var(--border-glass);
  border-radius: var(--radius-full);
  padding: 2px;
  gap: 2px;
  flex-shrink: 0;
}

.lang-btn {
  background: transparent;
  color: var(--text-secondary);
  border: none;
  padding: 0.28rem 0.55rem;
  border-radius: var(--radius-full);
  font-size: 0.78rem;
  font-weight: 700;
  cursor: pointer;
  display: inline-flex;
  align-items: center;
  gap: 0.25rem;
  transition: all var(--transition-fast);
  white-space: nowrap;
}

.lang-btn:hover {
  color: var(--text-primary);
  background-color: rgba(255, 255, 255, 0.08);
}

.lang-btn.active {
  background: var(--brand-gradient);
  color: #ffffff;
  box-shadow: 0 2px 8px rgba(56, 189, 248, 0.4);
}

.btn-icon {
  width: 40px;
  height: 40px;
  border-radius: var(--radius-sm);
  background-color: var(--bg-glass-card);
  border: 1px solid var(--border-glass);
  display: flex;
  align-items: center;
  justify-content: center;
  cursor: pointer;
  color: var(--text-secondary);
  transition: all var(--transition-fast);
}

.btn-icon:hover {
  color: var(--text-primary);
  border-color: var(--border-hover);
  transform: translateY(-2px);
}

.btn-primary {
  background: var(--brand-gradient);
  color: #ffffff;
  padding: 0.6rem 1.25rem;
  border-radius: var(--radius-sm);
  font-weight: 600;
  font-size: 0.95rem;
  cursor: pointer;
  display: inline-flex;
  align-items: center;
  gap: 0.5rem;
  box-shadow: var(--shadow-sm);
  transition: all var(--transition-fast);
}

.btn-primary:hover {
  transform: translateY(-2px);
  box-shadow: var(--brand-glow);
}

/* ==========================================================================
   Hero Section
   ========================================================================== */
.hero-section {
  padding: 4rem 1.5rem 3.25rem;
  text-align: center;
  position: relative;
}

.hero-container {
  max-width: 1080px;
  margin: 0 auto;
}

.seo-badge {
  display: inline-flex;
  align-items: center;
  gap: 0.5rem;
  background-color: var(--bg-glass-card);
  border: 1px solid var(--border-glass);
  padding: 0.35rem 1rem;
  border-radius: var(--radius-full);
  font-size: 0.85rem;
  font-weight: 600;
  color: var(--physics-accent);
  margin-bottom: 1.5rem;
  box-shadow: 0 8px 30px rgba(56, 189, 248, 0.08);
}

@keyframes pulseGlow {
  0%, 100% { box-shadow: 0 0 0 rgba(56, 189, 248, 0); }
  50% { box-shadow: 0 0 15px rgba(56, 189, 248, 0.3); }
}

.hero-title {
  max-width: 1050px;
  margin-inline: auto;
  font-size: clamp(2.25rem, 4.6vw, 3.65rem);
  font-weight: 900;
  line-height: 1.15;
  letter-spacing: -0.03em;
  margin-bottom: 1.25rem;
}

.hero-title .gradient-text {
  background: var(--brand-gradient);
  -webkit-background-clip: text;
  -webkit-text-fill-color: transparent;
}

.hero-subtitle {
  font-size: clamp(1.05rem, 2vw, 1.25rem);
  color: var(--text-secondary);
  max-width: 780px;
  margin: 0 auto 2.5rem;
  line-height: 1.6;
}

.hero-cta-group {
  display: flex;
  align-items: center;
  justify-content: center;
  gap: 1rem;
  flex-wrap: wrap;
  margin-bottom: 2.5rem;
}

.hero-cta-group > .btn-primary:nth-child(2) {
  color: var(--text-primary);
  background: rgba(56, 189, 248, 0.08);
  border: 1px solid rgba(56, 189, 248, 0.32);
  box-shadow: none;
}

.hero-cta-group > .btn-primary:nth-child(2):hover {
  background: rgba(56, 189, 248, 0.14);
}

.hero-stats {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(180px, 1fr));
  gap: 1rem;
  max-width: 960px;
  margin: 0 auto;
}

.stat-item {
  background-color: var(--bg-glass-card);
  border: 1px solid var(--border-glass);
  backdrop-filter: blur(12px);
  padding: 1rem 0.85rem;
  border-radius: var(--radius-md);
  text-align: center;
  transition: transform var(--transition-fast);
}

.stat-item:hover {
  transform: translateY(-4px);
  border-color: var(--border-hover);
}

.stat-num {
  font-size: 1.85rem;
  font-weight: 800;
  color: var(--text-primary);
  margin-bottom: 0.25rem;
}

.stat-label {
  font-size: 0.85rem;
  color: var(--text-secondary);
  line-height: 1.4;
}

.learning-quality-checklist {
  display: grid;
  gap: 0.55rem;
  padding: 0.85rem;
  color: var(--text-secondary);
  background: rgba(16, 185, 129, 0.07);
  border: 1px solid rgba(16, 185, 129, 0.2);
  border-radius: var(--radius-sm);
  font-size: 0.82rem;
}

.learning-quality-checklist span {
  display: flex;
  align-items: flex-start;
  gap: 0.5rem;
}

.learning-quality-checklist i {
  margin-top: 0.2rem;
  color: #34d399;
}

/* ==========================================================================
   Featured Direct Simulation Player (PhyLab Studio)
   ========================================================================== */
.featured-sim-section {
  padding: 2rem 1.5rem 4rem;
}

.section-container {
  max-width: 1280px;
  margin: 0 auto;
}

.section-header {
  margin-bottom: 2rem;
  display: flex;
  justify-content: space-between;
  align-items: flex-end;
  flex-wrap: wrap;
  gap: 1rem;
}

.section-title {
  font-size: 1.75rem;
  font-weight: 800;
  display: flex;
  align-items: center;
  gap: 0.75rem;
}

.section-tag {
  font-size: 0.75rem;
  text-transform: uppercase;
  letter-spacing: 0.08em;
  background-color: rgba(56, 189, 248, 0.15);
  color: var(--physics-accent);
  padding: 0.25rem 0.6rem;
  border-radius: var(--radius-sm);
}

.sim-player-card {
  background-color: var(--bg-secondary);
  border: 1px solid var(--border-glass);
  border-radius: var(--radius-lg);
  overflow: hidden;
  box-shadow: var(--shadow-lg);
}

.sim-player-bar {
  background-color: var(--bg-tertiary);
  padding: 0.85rem 1.5rem;
  display: flex;
  justify-content: space-between;
  align-items: center;
  border-bottom: 1px solid var(--border-glass);
}

.sim-meta-info {
  display: flex;
  align-items: center;
  gap: 1rem;
}

.live-indicator {
  display: flex;
  align-items: center;
  gap: 0.4rem;
  font-size: 0.8rem;
  font-weight: 700;
  color: #22c55e;
}

.live-dot {
  width: 8px;
  height: 8px;
  border-radius: 50%;
  background-color: #22c55e;
  box-shadow: 0 0 8px #22c55e;
  animation: blink 1.5s infinite;
}

@keyframes blink {
  0%, 100% { opacity: 1; }
  50% { opacity: 0.3; }
}

.sim-actions-bar {
  display: flex;
  gap: 0.5rem;
}

.sim-action-btn {
  background-color: var(--bg-glass-card);
  border: 1px solid var(--border-glass);
  color: var(--text-secondary);
  padding: 0.45rem 0.85rem;
  border-radius: var(--radius-sm);
  font-size: 0.85rem;
  font-weight: 500;
  cursor: pointer;
  display: flex;
  align-items: center;
  gap: 0.4rem;
  transition: all var(--transition-fast);
}

.sim-action-btn:hover {
  color: var(--text-primary);
  background-color: rgba(255, 255, 255, 0.1);
}

/* Fullscreen Player Styles */
.sim-player-card:fullscreen,
.sim-player-card:-webkit-full-screen,
.sim-player-card:-moz-full-screen {
  width: 100vw !important;
  height: 100vh !important;
  background: #020617 !important;
  display: flex !important;
  flex-direction: column !important;
  padding: 0 !important;
  margin: 0 !important;
  border-radius: 0 !important;
  border: none !important;
}

.sim-player-card:fullscreen .sim-player-bar,
.sim-player-card:-webkit-full-screen .sim-player-bar,
.sim-player-card:-moz-full-screen .sim-player-bar {
  background: #0f172a !important;
  border-bottom: 1px solid rgba(255, 255, 255, 0.1) !important;
  padding: 0.6rem 1.25rem !important;
  flex-shrink: 0 !important;
}

.sim-player-card:fullscreen .sim-frame-wrapper,
.sim-player-card:-webkit-full-screen .sim-frame-wrapper,
.sim-player-card:-moz-full-screen .sim-frame-wrapper {
  flex: 1 1 100% !important;
  height: calc(100vh - 54px) !important;
  max-height: calc(100vh - 54px) !important;
  border-radius: 0 !important;
  border: none !important;
}

.sim-player-card:fullscreen .sim-frame,
.sim-player-card:-webkit-full-screen .sim-frame,
.sim-player-card:-moz-full-screen .sim-frame {
  width: 100% !important;
  height: 100% !important;
}

/* Fallback Window Fullscreen */
.sim-player-card.is-window-fullscreen {
  position: fixed !important;
  top: 0 !important;
  left: 0 !important;
  width: 100vw !important;
  height: 100vh !important;
  z-index: 999999 !important;
  border-radius: 0 !important;
  background: #020617 !important;
  display: flex !important;
  flex-direction: column !important;
  margin: 0 !important;
  border: none !important;
}

.sim-player-card.is-window-fullscreen .sim-player-bar {
  background: #0f172a !important;
  border-bottom: 1px solid rgba(255, 255, 255, 0.1) !important;
  padding: 0.6rem 1.25rem !important;
  flex-shrink: 0 !important;
}

.sim-player-card.is-window-fullscreen .sim-frame-wrapper {
  flex: 1 1 100% !important;
  height: calc(100vh - 54px) !important;
  border-radius: 0 !important;
}

body.no-scroll {
  overflow: hidden !important;
}

.sim-frame-wrapper {
  position: relative;
  width: 100%;
  height: 680px;
  background-color: #000;
}

.sim-frame {
  width: 100%;
  height: 100%;
  border: none;
  transition: opacity var(--transition-normal);
}

.sim-frame-wrapper:not(.lab-frame-loaded) > .sim-frame[data-lab-src] {
  opacity: 0;
}

.lab-frame-launch {
  position: absolute;
  inset: 0;
  z-index: 2;
  display: grid;
  place-content: center;
  justify-items: center;
  gap: 1rem;
  padding: 1.5rem;
  text-align: center;
  background:
    radial-gradient(circle at 50% 35%, rgba(56, 189, 248, 0.18), transparent 34%),
    linear-gradient(145deg, #07111f, #0f172a 55%, #111827);
}

.lab-frame-launch-icon {
  font-size: clamp(2.25rem, 6vw, 4rem);
  color: var(--physics-accent);
  filter: drop-shadow(0 0 18px var(--physics-glow));
}

.lab-frame-launch-btn {
  min-height: 48px;
  padding: 0.8rem 1.25rem;
  border: 1px solid rgba(56, 189, 248, 0.55);
  border-radius: var(--radius-md);
  color: #f8fafc;
  background: linear-gradient(135deg, #0284c7, #7c3aed);
  box-shadow: 0 12px 30px rgba(2, 132, 199, 0.24);
  font: inherit;
  font-weight: 800;
  cursor: pointer;
}

.lab-frame-launch-btn:disabled {
  cursor: wait;
  opacity: 0.8;
}

.lab-frame-launch p {
  max-width: 480px;
  color: var(--text-secondary);
  font-size: 0.88rem;
}

.sim-features-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(280px, 1fr));
  gap: 1rem;
  padding: 1.5rem;
  background-color: var(--bg-secondary);
}

.sim-feature-box {
  background-color: var(--bg-glass-card);
  border: 1px solid var(--border-glass);
  border-radius: var(--radius-md);
  padding: 1rem 1.25rem;
  display: flex;
  gap: 1rem;
  align-items: flex-start;
}

.sim-feature-box i {
  font-size: 1.4rem;
  color: var(--physics-accent);
  margin-top: 0.2rem;
}

.sim-feature-box h4 {
  font-size: 0.95rem;
  font-weight: 700;
  margin-bottom: 0.2rem;
}

.sim-feature-box p {
  font-size: 0.82rem;
  color: var(--text-secondary);
  line-height: 1.4;
}

/* ==========================================================================
   STEM Subjects Hub & Filter
   ========================================================================== */
.subjects-hub-section {
  padding: 3rem 1.5rem 5rem;
}

.filter-bar {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 1rem;
  margin-bottom: 2.5rem;
  flex-wrap: wrap;
}

.filter-tabs {
  display: flex;
  gap: 0.5rem;
  background-color: var(--bg-glass-card);
  padding: 0.35rem;
  border-radius: var(--radius-md);
  border: 1px solid var(--border-glass);
  flex-wrap: wrap;
}

.filter-btn {
  padding: 0.5rem 1.15rem;
  border-radius: var(--radius-sm);
  background: transparent;
  font-size: 0.9rem;
  font-weight: 600;
  color: var(--text-secondary);
  cursor: pointer;
  transition: all var(--transition-fast);
  display: flex;
  align-items: center;
  gap: 0.45rem;
}

.filter-btn.active, .filter-btn:hover {
  color: var(--text-primary);
  background-color: var(--bg-tertiary);
}

.filter-btn.active {
  color: var(--subject-color, var(--text-primary));
}

.filter-btn[data-subject="physics"].active { color: var(--physics-accent); }
.filter-btn[data-subject="chemistry"].active { color: var(--chemistry-accent); }
.filter-btn[data-subject="math"].active { color: var(--math-accent); }
.filter-btn[data-subject="biology"].active { color: var(--biology-accent); }

.search-box {
  position: relative;
  min-width: 280px;
}

.search-input {
  width: 100%;
  background-color: var(--bg-glass-card);
  border: 1px solid var(--border-glass);
  padding: 0.6rem 1rem 0.6rem 2.5rem;
  border-radius: var(--radius-md);
  color: var(--text-primary);
  font-size: 0.9rem;
  transition: border-color var(--transition-fast);
}

.search-input:focus {
  border-color: var(--physics-accent);
}

.search-icon {
  position: absolute;
  left: 0.85rem;
  top: 50%;
  transform: translateY(-50%);
  color: var(--text-muted);
  font-size: 0.95rem;
}

.labs-grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(320px, 1fr));
  gap: 1.5rem;
}

.lab-card {
  background-color: var(--bg-glass-card);
  border: 1px solid var(--border-glass);
  backdrop-filter: blur(12px);
  border-radius: var(--radius-lg);
  padding: 1.5rem;
  display: flex;
  flex-direction: column;
  justify-content: space-between;
  transition: all var(--transition-normal);
  position: relative;
  overflow: hidden;
}

.lab-card::before {
  content: '';
  position: absolute;
  top: 0;
  left: 0;
  width: 100%;
  height: 4px;
  background: var(--card-accent, var(--physics-accent));
  opacity: 0.7;
}

.lab-card:hover {
  transform: translateY(-6px);
  border-color: var(--card-accent, var(--physics-accent));
  box-shadow: 0 12px 30px rgba(0, 0, 0, 0.4);
}

.lab-badge-row {
  display: flex;
  justify-content: space-between;
  align-items: center;
  margin-bottom: 1rem;
}

.subject-badge {
  font-size: 0.75rem;
  font-weight: 700;
  padding: 0.2rem 0.6rem;
  border-radius: var(--radius-full);
  text-transform: uppercase;
  letter-spacing: 0.05em;
}

.subject-badge {
  color: var(--subject-color, var(--text-primary));
  background: var(--subject-glow, rgba(148, 163, 184, 0.14));
}

.badge-physics { background: var(--physics-glow); color: var(--physics-accent); }
.badge-chemistry { background: var(--chemistry-glow); color: var(--chemistry-accent); }
.badge-math { background: var(--math-glow); color: var(--math-accent); }
.badge-biology { background: var(--biology-glow); color: var(--biology-accent); }

.grade-level {
  font-size: 0.75rem;
  color: var(--text-muted);
  font-weight: 500;
}

.lab-title {
  font-size: 1.25rem;
  font-weight: 700;
  margin-bottom: 0.6rem;
  line-height: 1.35;
}

.lab-desc {
  font-size: 0.88rem;
  color: var(--text-secondary);
  margin-bottom: 1.25rem;
  line-height: 1.5;
  flex-grow: 1;
}

.lab-tags {
  display: flex;
  flex-wrap: wrap;
  gap: 0.4rem;
  margin-bottom: 1.25rem;
}

.lab-tag {
  font-size: 0.72rem;
  background-color: rgba(255, 255, 255, 0.05);
  color: var(--text-muted);
  padding: 0.15rem 0.5rem;
  border-radius: var(--radius-sm);
}

.lab-footer {
  display: flex;
  align-items: center;
  justify-content: space-between;
  border-top: 1px solid var(--border-glass);
  padding-top: 1rem;
}

.lab-open-btn {
  font-size: 0.88rem;
  font-weight: 600;
  color: var(--card-accent, var(--physics-accent));
  display: flex;
  align-items: center;
  gap: 0.35rem;
  transition: transform var(--transition-fast);
}

.lab-card:hover .lab-open-btn {
  transform: translateX(4px);
}

/* ==========================================================================
   SEO & AI Knowledge Hub Section (GEO Rich Data)
   ========================================================================== */
.seo-knowledge-section {
  padding: 4rem 1.5rem;
  background: linear-gradient(180deg, transparent 0%, var(--bg-secondary) 100%);
  border-top: 1px solid var(--border-glass);
}

.seo-card-container {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(320px, 1fr));
  gap: 1.5rem;
}

.seo-info-card {
  background-color: var(--bg-glass-card);
  border: 1px solid var(--border-glass);
  border-radius: var(--radius-lg);
  padding: 1.75rem;
}

.seo-info-card h3 {
  font-size: 1.2rem;
  margin-bottom: 0.85rem;
  display: flex;
  align-items: center;
  gap: 0.5rem;
}

.seo-info-card p {
  color: var(--text-secondary);
  font-size: 0.9rem;
  margin-bottom: 1rem;
  line-height: 1.6;
}

.faq-list {
  list-style: none;
  display: flex;
  flex-direction: column;
  gap: 1rem;
}

.faq-item {
  background-color: rgba(255, 255, 255, 0.03);
  border: 1px solid var(--border-glass);
  border-radius: var(--radius-md);
  padding: 1rem;
}

.faq-question {
  font-weight: 600;
  font-size: 0.95rem;
  margin-bottom: 0.4rem;
  color: var(--text-primary);
}

.faq-answer {
  font-size: 0.85rem;
  color: var(--text-secondary);
  line-height: 1.5;
}

/* ==========================================================================
   Interactive Lab Experiment Modal
   ========================================================================== */
.modal-overlay {
  position: fixed;
  top: 0;
  left: 0;
  width: 100vw;
  height: 100vh;
  background-color: rgba(0, 0, 0, 0.85);
  backdrop-filter: blur(8px);
  z-index: 1000;
  display: none;
  align-items: center;
  justify-content: center;
  padding: 1.5rem;
}

.modal-overlay.active {
  display: flex;
}

.modal-content {
  background-color: var(--bg-secondary);
  border: 1px solid var(--border-glass);
  border-radius: var(--radius-lg);
  width: 100%;
  max-width: 1200px;
  height: 90vh;
  display: flex;
  flex-direction: column;
  overflow: hidden;
  box-shadow: var(--shadow-lg);
}

.modal-header {
  background-color: var(--bg-tertiary);
  padding: 0.85rem 1.5rem;
  display: flex;
  align-items: center;
  justify-content: space-between;
  border-bottom: 1px solid var(--border-glass);
}

.modal-title {
  font-size: 1.15rem;
  font-weight: 700;
  display: flex;
  align-items: center;
  gap: 0.6rem;
}

.modal-body {
  flex-grow: 1;
  display: flex;
  overflow: hidden;
}

.modal-frame-container {
  flex: 3;
  height: 100%;
  background-color: #000;
}

.modal-sidebar {
  flex: 1.2;
  background-color: var(--bg-primary);
  border-left: 1px solid var(--border-glass);
  display: flex;
  flex-direction: column;
  overflow-y: auto;
  padding: 1.25rem;
  gap: 1.25rem;
}

.sidebar-block h4 {
  font-size: 0.95rem;
  font-weight: 700;
  margin-bottom: 0.5rem;
  color: var(--physics-accent);
}

.lab-notes-area {
  width: 100%;
  height: 140px;
  background-color: var(--bg-glass-card);
  border: 1px solid var(--border-glass);
  border-radius: var(--radius-sm);
  padding: 0.75rem;
  color: var(--text-primary);
  font-size: 0.85rem;
  resize: vertical;
}

/* ==========================================================================
   Footer
   ========================================================================== */
.site-footer {
  background-color: var(--bg-secondary);
  border-top: 1px solid var(--border-glass);
  padding: 3.5rem 1.5rem 1.5rem;
  margin-top: auto;
}

.footer-container {
  max-width: 1280px;
  margin: 0 auto;
  display: grid;
  grid-template-columns: 2fr repeat(3, 1fr);
  gap: 2.5rem;
  margin-bottom: 2.5rem;
}

.footer-brand p {
  color: var(--text-secondary);
  font-size: 0.88rem;
  margin-top: 0.85rem;
  max-width: 340px;
}

.footer-col h4 {
  font-size: 0.95rem;
  font-weight: 700;
  margin-bottom: 1rem;
  color: var(--text-primary);
}

.footer-col ul {
  list-style: none;
  display: flex;
  flex-direction: column;
  gap: 0.6rem;
}

.footer-col a {
  color: var(--text-secondary);
  font-size: 0.85rem;
}

.footer-col a:hover {
  color: var(--physics-accent);
}

.footer-bottom {
  max-width: 1280px;
  margin: 0 auto;
  border-top: 1px solid var(--border-glass);
  padding-top: 1.5rem;
  display: flex;
  justify-content: space-between;
  align-items: center;
  color: var(--text-muted);
  font-size: 0.82rem;
  flex-wrap: wrap;
  gap: 1rem;
}

/* ==========================================================================
   Responsive Breakpoints
   ========================================================================== */
/* ==========================================================================
   Donation & Support Styles (PayPal & Techcombank VietQR)
   ========================================================================== */
.btn-donate {
  background: linear-gradient(135deg, #f43f5e 0%, #fb7185 100%);
  color: #ffffff;
  padding: 0.45rem 1rem;
  border-radius: var(--radius-sm);
  font-weight: 700;
  font-size: 0.85rem;
  cursor: pointer;
  display: inline-flex;
  align-items: center;
  gap: 0.4rem;
  box-shadow: 0 4px 15px rgba(244, 63, 94, 0.35);
  transition: all var(--transition-fast);
  border: 1px solid rgba(255, 255, 255, 0.2);
  white-space: nowrap !important;
  flex-shrink: 0 !important;
}

.btn-donate:hover {
  transform: translateY(-2px);
  box-shadow: 0 6px 20px rgba(244, 63, 94, 0.5);
  background: linear-gradient(135deg, #e11d48 0%, #f43f5e 100%);
}

.floating-donate-btn {
  position: fixed;
  bottom: 1.5rem;
  right: 1.5rem;
  z-index: 99;
  background: linear-gradient(135deg, #f43f5e 0%, #fb7185 100%);
  color: #fff;
  padding: 0.65rem 1.25rem;
  border-radius: var(--radius-full);
  box-shadow: 0 8px 25px rgba(244, 63, 94, 0.45);
  font-weight: 700;
  font-size: 0.9rem;
  display: flex;
  align-items: center;
  gap: 0.45rem;
  cursor: pointer;
  transition: all var(--transition-fast);
  border: 2px solid rgba(255, 255, 255, 0.3);
  animation: heartPulse 2.5s infinite;
  white-space: nowrap !important;
}

@keyframes heartPulse {
  0%, 100% { transform: scale(1); }
  50% { transform: scale(1.04); box-shadow: 0 10px 30px rgba(244, 63, 94, 0.6); }
}

.floating-donate-btn:hover {
  transform: translateY(-3px) scale(1.05);
}

/* Author Profile & Credentials Section */
.author-profile-section {
  padding: 3.5rem 1.5rem;
  background: linear-gradient(180deg, transparent 0%, rgba(15, 23, 42, 0.6) 100%);
  position: relative;
}

.author-profile-card {
  background: var(--bg-glass-card);
  border: 1px solid var(--border-glass);
  border-radius: var(--radius-lg);
  padding: 2.25rem;
  box-shadow: var(--shadow-glass);
  backdrop-filter: blur(16px);
  -webkit-backdrop-filter: blur(16px);
  display: grid;
  grid-template-columns: 1fr;
  gap: 2rem;
  position: relative;
  overflow: hidden;
}

@media (min-width: 992px) {
  .author-profile-card {
    grid-template-columns: 320px 1fr;
    gap: 2.5rem;
  }
}

.author-profile-card::before {
  content: '';
  position: absolute;
  top: 0;
  left: 0;
  right: 0;
  height: 3px;
  background: linear-gradient(90deg, #38bdf8 0%, #a855f7 50%, #f43f5e 100%);
}

.author-avatar-wrap {
  display: flex;
  flex-direction: column;
  align-items: center;
  text-align: center;
  padding: 1.5rem;
  background: rgba(255, 255, 255, 0.03);
  border: 1px solid rgba(255, 255, 255, 0.06);
  border-radius: var(--radius-md);
}

.author-avatar-icon {
  width: 90px;
  height: 90px;
  border-radius: 50%;
  background: linear-gradient(135deg, #0284c7 0%, #38bdf8 100%);
  display: flex;
  align-items: center;
  justify-content: center;
  color: #fff;
  font-size: 2.5rem;
  box-shadow: 0 0 25px rgba(56, 189, 248, 0.45);
  margin-bottom: 1rem;
  border: 3px solid rgba(255, 255, 255, 0.2);
}

.author-exp-badge {
  display: inline-flex;
  align-items: center;
  gap: 0.4rem;
  background: rgba(34, 197, 94, 0.15);
  border: 1px solid rgba(34, 197, 94, 0.35);
  color: #4ade80;
  padding: 0.35rem 0.85rem;
  border-radius: 999px;
  font-size: 0.82rem;
  font-weight: 700;
  margin-top: 0.75rem;
}

.author-details-content {
  display: flex;
  flex-direction: column;
  justify-content: center;
}

.author-edu-list {
  display: flex;
  flex-wrap: wrap;
  gap: 0.75rem;
  margin: 1rem 0 1.25rem;
}

.author-edu-item {
  display: inline-flex;
  align-items: center;
  gap: 0.5rem;
  background: rgba(56, 189, 248, 0.1);
  border: 1px solid rgba(56, 189, 248, 0.3);
  color: #38bdf8;
  padding: 0.45rem 0.9rem;
  border-radius: var(--radius-sm);
  font-size: 0.85rem;
  font-weight: 700;
}

.author-fields-grid {
  display: grid;
  grid-template-columns: 1fr;
  gap: 0.85rem;
  margin-top: 1.25rem;
}

@media (min-width: 640px) {
  .author-fields-grid {
    grid-template-columns: repeat(3, 1fr);
  }
}

.author-field-card {
  background: rgba(255, 255, 255, 0.03);
  border: 1px solid rgba(255, 255, 255, 0.08);
  border-radius: var(--radius-sm);
  padding: 1rem;
  transition: all var(--transition-fast);
}

.author-field-card:hover {
  background: rgba(255, 255, 255, 0.06);
  border-color: rgba(56, 189, 248, 0.4);
  transform: translateY(-2px);
}

.author-field-card h5 {
  font-size: 0.9rem;
  font-weight: 700;
  color: var(--text-primary);
  margin-bottom: 0.4rem;
  display: flex;
  align-items: center;
  gap: 0.45rem;
}

/* Anti-Scraping & Content Protection Rules */
.sim-player-card,
.brand-logo,
.sim-actions-bar {
  -webkit-user-select: none;
  -moz-user-select: none;
  -ms-user-select: none;
  user-select: none;
  -webkit-touch-callout: none;
}

input, textarea, [contenteditable="true"] {
  -webkit-user-select: text !important;
  -moz-user-select: text !important;
  -ms-user-select: text !important;
  user-select: text !important;
}

/* Donate Modal */
.donate-modal-content {
  width: 100%;
  max-width: 780px;
  max-height: 90vh;
  background-color: var(--bg-secondary);
  border-radius: var(--radius-lg);
  border: 1px solid var(--border-glass);
  box-shadow: var(--shadow-lg);
  overflow-y: auto;
  overflow-x: hidden;
  display: flex;
  flex-direction: column;
  -webkit-overflow-scrolling: touch;
}

@media (max-width: 768px) {
  .modal-overlay {
    padding: 0.75rem;
    align-items: flex-start;
  }
  .donate-modal-content {
    max-height: 94vh;
    margin: auto 0;
  }
}

.donate-header {
  background: linear-gradient(135deg, rgba(244, 63, 94, 0.15), rgba(168, 85, 247, 0.15));
  border-bottom: 1px solid var(--border-glass);
  padding: 1.25rem 1.75rem;
  display: flex;
  justify-content: space-between;
  align-items: center;
}

.donate-tabs {
  display: flex;
  gap: 0.5rem;
  background-color: var(--bg-glass-card);
  padding: 0.35rem;
  border-radius: var(--radius-md);
  margin: 1.25rem 1.75rem 0.5rem;
  border: 1px solid var(--border-glass);
}

.donate-tab-btn {
  flex: 1;
  padding: 0.6rem;
  border-radius: var(--radius-sm);
  background: transparent;
  color: var(--text-secondary);
  font-weight: 700;
  font-size: 0.95rem;
  cursor: pointer;
  display: flex;
  align-items: center;
  justify-content: center;
  gap: 0.5rem;
  transition: all var(--transition-fast);
}

.donate-tab-btn.active {
  background-color: var(--bg-tertiary);
  color: var(--text-primary);
  box-shadow: var(--shadow-sm);
}

.donate-tab-btn[data-tab="paypal"].active {
  color: #0079C1;
}

.donate-tab-btn[data-tab="bank"].active {
  color: #E21A22;
}

.donate-body {
  padding: 1.5rem 1.75rem 2rem;
}

.donate-panel {
  display: none;
  grid-template-columns: 1fr 1.2fr;
  gap: 1.75rem;
  align-items: center;
}

.donate-panel.active {
  display: grid;
}

.donate-panel-full {
  grid-template-columns: 1fr !important;
}

.paypal-direct-card {
  background: linear-gradient(135deg, rgba(0, 121, 193, 0.12) 0%, rgba(0, 48, 135, 0.25) 100%);
  border: 1px solid rgba(0, 121, 193, 0.4);
  border-radius: var(--radius-lg);
  padding: 2rem;
  text-align: center;
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: 1.25rem;
  box-shadow: 0 8px 30px rgba(0, 121, 193, 0.2);
}

.paypal-avatar-badge {
  width: 72px;
  height: 72px;
  border-radius: 50%;
  background: linear-gradient(135deg, #0079C1 0%, #00457C 100%);
  color: #fff;
  font-size: 2.2rem;
  display: flex;
  align-items: center;
  justify-content: center;
  box-shadow: 0 4px 20px rgba(0, 121, 193, 0.5);
  border: 3px solid rgba(255, 255, 255, 0.2);
}

.paypal-tag-name {
  font-size: 1.4rem;
  font-weight: 800;
  color: #38bdf8;
  font-family: var(--font-mono);
  letter-spacing: -0.01em;
}

.btn-paypal-direct {
  background: linear-gradient(135deg, #0079C1 0%, #00457C 100%);
  color: #ffffff !important;
  padding: 0.9rem 2rem;
  border-radius: var(--radius-full);
  font-weight: 800;
  font-size: 1.05rem;
  display: inline-flex;
  align-items: center;
  gap: 0.6rem;
  box-shadow: 0 6px 25px rgba(0, 121, 193, 0.45);
  transition: all var(--transition-fast);
  border: 1px solid rgba(255, 255, 255, 0.3);
  text-decoration: none;
}

/* Amount Selector & Quick Chips */
.donation-amount-group {
  width: 100%;
  max-width: 520px;
  display: flex;
  flex-direction: column;
  gap: 0.85rem;
}

.amount-chips {
  display: grid;
  grid-template-columns: repeat(4, 1fr);
  gap: 0.6rem;
}

.amount-chip {
  background-color: var(--bg-glass-card);
  border: 1px solid var(--border-glass);
  padding: 0.6rem 0.35rem;
  border-radius: var(--radius-md);
  color: var(--text-primary);
  font-weight: 700;
  font-size: 0.95rem;
  cursor: pointer;
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: 0.2rem;
  transition: all var(--transition-fast);
}

.amount-chip span {
  font-size: 0.72rem;
  font-weight: 500;
  color: var(--text-muted);
}

.amount-chip:hover {
  border-color: var(--physics-accent);
  background-color: rgba(56, 189, 248, 0.1);
  transform: translateY(-2px);
}

.amount-chip.active {
  background: var(--brand-gradient);
  color: #fff;
  border-color: transparent;
  box-shadow: 0 4px 15px rgba(56, 189, 248, 0.4);
}

.amount-chip.active span {
  color: rgba(255, 255, 255, 0.85);
}

.custom-amount-input-wrap {
  position: relative;
  display: flex;
  align-items: center;
}

.custom-amount-input {
  width: 100%;
  background-color: var(--bg-glass-card);
  border: 1px solid var(--border-glass);
  padding: 0.75rem 3.5rem 0.75rem 2.5rem;
  border-radius: var(--radius-md);
  color: var(--text-primary);
  font-size: 1.1rem;
  font-weight: 800;
  font-family: var(--font-mono);
  transition: all var(--transition-fast);
}

.custom-amount-input:focus {
  border-color: var(--physics-accent);
  box-shadow: 0 0 15px rgba(56, 189, 248, 0.25);
}

.amount-currency-symbol {
  position: absolute;
  left: 1rem;
  font-weight: 800;
  color: var(--physics-accent);
  font-size: 1.1rem;
}

.amount-currency-unit {
  position: absolute;
  right: 1rem;
  font-weight: 700;
  font-size: 0.85rem;
  color: var(--text-muted);
}

.qr-box-card {
  background: #ffffff;
  padding: 1rem;
  border-radius: var(--radius-md);
  box-shadow: var(--shadow-md);
  text-align: center;
}

.qr-image {
  width: 100%;
  max-width: 260px;
  height: auto;
  border-radius: var(--radius-sm);
  display: block;
  margin: 0 auto;
}

.donate-info-details {
  display: flex;
  flex-direction: column;
  gap: 0.85rem;
}

.donate-info-row {
  background-color: var(--bg-glass-card);
  border: 1px solid var(--border-glass);
  padding: 0.75rem 1rem;
  border-radius: var(--radius-md);
  display: flex;
  justify-content: space-between;
  align-items: center;
  gap: 0.5rem;
}

.donate-label {
  font-size: 0.8rem;
  color: var(--text-muted);
  text-transform: uppercase;
  letter-spacing: 0.05em;
}

.donate-val {
  font-size: 0.95rem;
  font-weight: 700;
  color: var(--text-primary);
  font-family: var(--font-mono);
}

.copy-badge-btn {
  background-color: rgba(56, 189, 248, 0.15);
  color: var(--physics-accent);
  padding: 0.3rem 0.65rem;
  border-radius: var(--radius-sm);
  font-size: 0.78rem;
  font-weight: 600;
  cursor: pointer;
  display: flex;
  align-items: center;
  gap: 0.35rem;
  transition: all var(--transition-fast);
  border: 1px solid rgba(56, 189, 248, 0.3);
}

.copy-badge-btn:hover {
  background-color: var(--physics-accent);
  color: #000;
}

.copy-badge-btn.copied {
  background-color: #22c55e;
  color: #fff;
  border-color: #22c55e;
}

.preset-note-box {
  background: rgba(244, 63, 94, 0.1);
  border: 1px dashed rgba(244, 63, 94, 0.4);
  padding: 0.85rem 1rem;
  border-radius: var(--radius-md);
}

.preset-note-title {
  font-size: 0.78rem;
  font-weight: 700;
  color: var(--chemistry-accent);
  margin-bottom: 0.25rem;
  display: flex;
  align-items: center;
  gap: 0.35rem;
}

.preset-note-text {
  font-size: 0.95rem;
  font-weight: 700;
  color: var(--text-primary);
  display: flex;
  justify-content: space-between;
  align-items: center;
}

@media (max-width: 768px) {
  .donate-panel {
    grid-template-columns: 1fr;
  }
  .floating-donate-btn {
    bottom: 1rem;
    right: 1rem;
    padding: 0.6rem 1rem;
    font-size: 0.85rem;
  }
}


@media (max-width: 768px) {
  .nav-links {
    display: none;
  }
  .sim-frame-wrapper {
    height: 460px;
  }
  .filter-bar {
    flex-direction: column;
    align-items: stretch;
  }
  .footer-container {
    grid-template-columns: 1fr;
  }
}

/* ==========================================================================
   Educational Purpose & Student Lookup Hub Styles
   ========================================================================== */
.mission-section {
  padding: 5rem 0 3rem;
  position: relative;
}

.mission-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(280px, 1fr));
  gap: 1.5rem;
  margin-top: 2.5rem;
}

.mission-card {
  background: var(--bg-glass-card);
  backdrop-filter: blur(16px);
  -webkit-backdrop-filter: blur(16px);
  border: 1px solid var(--border-glass);
  border-radius: var(--radius-lg);
  padding: 1.8rem;
  display: flex;
  flex-direction: column;
  gap: 1rem;
  transition: all var(--transition-normal);
  position: relative;
  overflow: hidden;
}

.mission-card::before {
  content: '';
  position: absolute;
  top: 0;
  left: 0;
  right: 0;
  height: 3px;
  background: var(--card-accent, var(--brand-gradient));
  opacity: 0.7;
  transition: height 0.3s ease, opacity 0.3s ease;
}

.mission-card:hover {
  transform: translateY(-6px);
  border-color: var(--border-hover);
  box-shadow: var(--shadow-lg);
}

.mission-card:hover::before {
  height: 5px;
  opacity: 1;
}

.mission-card-icon {
  width: 52px;
  height: 52px;
  border-radius: var(--radius-md);
  background: rgba(255, 255, 255, 0.05);
  border: 1px solid var(--border-glass);
  display: flex;
  align-items: center;
  justify-content: center;
  font-size: 1.5rem;
}

.mission-card-title {
  font-size: 1.2rem;
  font-weight: 800;
  color: var(--text-primary);
  line-height: 1.35;
}

.mission-card-desc {
  font-size: 0.9rem;
  color: var(--text-secondary);
  line-height: 1.6;
}

.mission-card-points {
  display: flex;
  flex-direction: column;
  gap: 0.5rem;
  font-size: 0.84rem;
  color: var(--text-muted);
  list-style: none;
  margin-top: auto;
  padding-top: 0.8rem;
  border-top: 1px solid rgba(255, 255, 255, 0.06);
}

.mission-card-points li {
  display: flex;
  align-items: flex-start;
  gap: 0.5rem;
  line-height: 1.5;
}

.mission-card-points li i {
  margin-top: 3px;
  font-size: 0.8rem;
  flex-shrink: 0;
}

/* Quick Subject Lookup Directory */
.lookup-portal-section {
  padding: 3rem 0 5rem;
}

.lookup-portal-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(280px, 1fr));
  gap: 1.5rem;
  margin-top: 2rem;
}

.lookup-subject-card {
  background: var(--bg-glass-card);
  backdrop-filter: blur(16px);
  -webkit-backdrop-filter: blur(16px);
  border: 1px solid var(--border-glass);
  border-radius: var(--radius-lg);
  padding: 1.6rem;
  display: flex;
  flex-direction: column;
  transition: all var(--transition-normal);
  position: relative;
}

.lookup-subject-card:hover {
  transform: translateY(-5px);
  box-shadow: 0 15px 35px var(--subject-glow, rgba(0,0,0,0.4));
  border-color: var(--subject-accent, var(--border-hover));
}

.lookup-subject-header {
  display: flex;
  align-items: center;
  gap: 0.85rem;
  margin-bottom: 1rem;
}

.lookup-subject-icon {
  width: 44px;
  height: 44px;
  border-radius: var(--radius-md);
  display: flex;
  align-items: center;
  justify-content: center;
  font-size: 1.3rem;
  background: rgba(255, 255, 255, 0.05);
}

.lookup-subject-title {
  font-size: 1.15rem;
  font-weight: 800;
  color: var(--text-primary);
}

.lookup-subject-badge {
  font-size: 0.72rem;
  font-weight: 700;
  text-transform: uppercase;
  letter-spacing: 0.05em;
  padding: 2px 8px;
  border-radius: var(--radius-full);
}

.lookup-links-list {
  display: flex;
  flex-direction: column;
  gap: 0.55rem;
  margin: 1rem 0 1.25rem;
  flex: 1;
}

.lookup-link-item {
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: 0.55rem 0.85rem;
  background: rgba(0, 0, 0, 0.2);
  border: 1px solid rgba(255, 255, 255, 0.05);
  border-radius: var(--radius-sm);
  font-size: 0.84rem;
  color: var(--text-secondary);
  transition: all var(--transition-fast);
}

.lookup-link-item:hover {
  background: rgba(255, 255, 255, 0.08);
  color: #fff;
  border-color: var(--subject-accent, #38bdf8);
  transform: translateX(4px);
}

.lookup-link-item i {
  font-size: 0.75rem;
  color: var(--subject-accent, #38bdf8);
}

.lookup-action-btn {
  width: 100%;
  padding: 0.65rem 1rem;
  border-radius: var(--radius-sm);
  font-size: 0.86rem;
  font-weight: 700;
  display: flex;
  align-items: center;
  justify-content: center;
  gap: 0.5rem;
  background: var(--subject-btn-bg, rgba(56, 189, 248, 0.15));
  color: var(--subject-accent, #38bdf8);
  border: 1px solid var(--subject-accent, #38bdf8);
  cursor: pointer;
  transition: all var(--transition-fast);
}

.lookup-action-btn:hover {
  background: var(--subject-accent, #38bdf8);
  color: #000;
}

/* ==========================================================================
   Subject Specific Learning Purpose & Quick Reference Styles
   ========================================================================== */
.subject-purpose-section {
  padding: 3.5rem 0 2rem;
  background: rgba(0, 0, 0, 0.15);
  border-top: 1px solid var(--border-glass);
  border-bottom: 1px solid var(--border-glass);
}

.subject-purpose-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(300px, 1fr));
  gap: 1.5rem;
  margin-top: 1.8rem;
}

.purpose-box {
  background: var(--bg-glass-card);
  backdrop-filter: blur(16px);
  -webkit-backdrop-filter: blur(16px);
  border: 1px solid var(--border-glass);
  border-radius: var(--radius-lg);
  padding: 1.6rem;
  display: flex;
  flex-direction: column;
  gap: 0.85rem;
  transition: all var(--transition-normal);
}

.purpose-box:hover {
  transform: translateY(-4px);
  border-color: var(--box-accent, var(--physics-accent));
  box-shadow: 0 12px 30px rgba(0, 0, 0, 0.35);
}

.purpose-box-header {
  display: flex;
  align-items: center;
  gap: 0.75rem;
}

.purpose-box-icon {
  width: 42px;
  height: 42px;
  border-radius: var(--radius-md);
  display: flex;
  align-items: center;
  justify-content: center;
  font-size: 1.25rem;
  background: rgba(255, 255, 255, 0.05);
  border: 1px solid var(--border-glass);
  color: var(--box-accent, var(--physics-accent));
}

.purpose-box-title {
  font-size: 1.1rem;
  font-weight: 800;
  color: var(--text-primary);
}

.purpose-box-desc {
  font-size: 0.88rem;
  color: var(--text-secondary);
  line-height: 1.6;
}

.purpose-box-list {
  list-style: none;
  display: flex;
  flex-direction: column;
  gap: 0.45rem;
  font-size: 0.84rem;
  color: var(--text-muted);
  margin-top: auto;
  padding-top: 0.75rem;
  border-top: 1px solid rgba(255, 255, 255, 0.06);
}

.purpose-box-list li {
  display: flex;
  align-items: flex-start;
  gap: 0.5rem;
  line-height: 1.45;
}

.purpose-box-list li i {
  color: var(--box-accent, var(--physics-accent));
  font-size: 0.75rem;
  margin-top: 3px;
  flex-shrink: 0;
}

/* ========================================================================== 
   Mobile & Tablet Learning Experience
   ========================================================================== */
@media (max-width: 1100px) {
  .nav-container {
    position: relative;
  }

  .mobile-menu-toggle {
    display: inline-grid;
    order: 2;
  }

  .nav-container > .primary-navigation {
    position: absolute;
    top: calc(100% + 1px);
    left: 0.75rem;
    right: 0.75rem;
    display: none;
    padding: 0.65rem;
    background: color-mix(in srgb, var(--bg-secondary) 96%, transparent);
    border: 1px solid var(--border-glass);
    border-radius: 0 0 var(--radius-md) var(--radius-md);
    box-shadow: var(--shadow-md);
    backdrop-filter: blur(18px);
  }

  .navbar.mobile-open .primary-navigation {
    display: block;
  }

  .primary-navigation .nav-links {
    display: flex !important;
    flex-direction: column;
    align-items: stretch;
    gap: 0.25rem;
  }

  .primary-navigation .nav-item a {
    min-height: 48px;
    padding: 0.75rem 0.9rem;
    font-size: 0.95rem;
  }

  .nav-actions {
    order: 3;
    margin-left: auto;
  }

  .nav-actions > .btn-primary,
  .nav-actions > .btn-donate {
    display: none;
  }

  .filter-tabs {
    max-width: 100%;
    flex-wrap: nowrap;
    overflow-x: auto;
    overscroll-behavior-inline: contain;
    scrollbar-width: thin;
    scroll-snap-type: x proximity;
    -webkit-overflow-scrolling: touch;
  }

  .filter-btn {
    flex: 0 0 auto;
    min-height: 44px;
    scroll-snap-align: start;
  }
}

@media (max-width: 800px) {
  .hero-section {
    padding-inline: 1rem;
  }

  .seo-badge {
    max-width: 100%;
    justify-content: center;
    white-space: normal;
    line-height: 1.4;
  }

  .hero-title {
    font-size: clamp(2rem, 9vw, 3rem);
    line-height: 1.12;
  }

  .hero-cta-group > * {
    width: 100% !important;
    min-height: 48px;
    justify-content: center;
  }

  .hero-stats {
    grid-template-columns: repeat(2, minmax(0, 1fr));
    gap: 0.75rem;
  }

  .labs-grid,
  .lookup-portal-grid,
  .mission-grid,
  .seo-card-container,
  .subject-purpose-grid {
    grid-template-columns: minmax(0, 1fr);
  }

  .labs-grid {
    gap: 1rem;
  }

  .lab-card,
  .lookup-subject-card,
  .mission-card,
  .seo-info-card,
  .purpose-box {
    padding: 1.1rem;
  }

  .lab-open-btn,
  .lookup-link-item,
  .sim-action-btn,
  .btn-primary,
  .btn-icon {
    min-height: 44px;
  }

  .modal-overlay {
    padding: 0;
  }

  .modal-content {
    width: 100vw;
    max-width: none;
    height: 100dvh;
    max-height: none;
    border: 0;
    border-radius: 0;
  }

  .modal-header {
    position: sticky;
    top: 0;
    z-index: 3;
    gap: 0.5rem;
    padding: max(0.55rem, env(safe-area-inset-top)) 0.7rem 0.55rem;
  }

  .modal-title {
    min-width: 0;
    overflow: hidden;
    font-size: 0.92rem;
    text-overflow: ellipsis;
    white-space: nowrap;
  }

  .modal-header button,
  #closeModalBtn {
    width: 44px !important;
    min-width: 44px;
    height: 44px !important;
    padding: 0;
    justify-content: center;
  }

  .modal-body {
    flex-direction: column;
    overflow-x: hidden;
    overflow-y: auto;
    -webkit-overflow-scrolling: touch;
  }

  .modal-frame-container {
    flex: 0 0 auto;
    width: 100%;
    height: 68dvh;
    min-height: 430px;
  }

  .modal-sidebar {
    flex: 0 0 auto;
    width: 100%;
    border-top: 1px solid var(--border-glass);
    border-left: 0;
    padding: 1rem;
  }

  .sim-frame-wrapper {
    height: min(72dvh, 680px) !important;
    min-height: 500px;
  }

  body.modal-open {
    overflow: hidden;
    touch-action: none;
  }

  .floating-donate-btn {
    right: max(0.75rem, env(safe-area-inset-right));
    bottom: max(0.75rem, env(safe-area-inset-bottom));
    width: 48px;
    height: 48px;
    justify-content: center;
    padding: 0;
    border-width: 1px;
    animation: none;
  }

  .floating-donate-btn span {
    display: none;
  }
}

@media (max-width: 560px) {
  .nav-container {
    padding-inline: 0.7rem;
  }

  .brand-name,
  .nav-back-pill span,
  .lang-btn span:first-child {
    display: none;
  }

  .brand-logo {
    gap: 0;
  }

  .nav-actions {
    gap: 0.35rem;
  }

  .lang-btn {
    min-width: 38px;
    min-height: 38px;
    justify-content: center;
    padding-inline: 0.4rem;
  }

  .subjects-hub-section,
  .lookup-portal-section,
  .mission-section,
  .seo-knowledge-section,
  .subject-purpose-section,
  .featured-sim-section {
    padding-inline: 0.85rem;
  }

  .filter-bar {
    margin-bottom: 1.25rem;
  }

  .search-box {
    min-width: 0;
    width: 100%;
  }

  .search-input {
    min-height: 48px;
    font-size: 1rem;
  }

  .lab-badge-row {
    align-items: flex-start;
    gap: 0.6rem;
  }

  .grade-level {
    text-align: right;
  }

  .stat-item {
    min-width: 0;
    padding: 0.85rem 0.5rem;
  }

  .stat-num {
    font-size: 1.45rem;
  }

  .stat-label {
    font-size: 0.74rem;
  }

  .learning-topic-section-header {
    align-items: stretch;
    flex-direction: column;
  }

  .learning-topic-tools {
    width: 100%;
  }

  .learning-readiness {
    padding-inline: 0.8rem;
  }

  .learning-readiness ul {
    display: grid;
    grid-template-columns: repeat(2, minmax(0, 1fr));
  }

  .learning-readiness li {
    border-radius: var(--radius-sm);
  }
}

@media (hover: none) {
  .lab-card:hover,
  .lookup-subject-card:hover,
  .mission-card:hover,
  .purpose-box:hover {
    transform: none;
  }

  .lab-card:hover .lab-open-btn {
    transform: none;
  }
}