:root {
  /* Clean, Calm Study Light Theme (Default) */
  --bg: #f4f6f9;
  --bg-sidebar: #ffffff;
  --bg-card: #ffffff;
  --bg-soft: #f8fafc;
  --bg-hover: #f1f5f9;
  --text: #111827;
  --text-secondary: #374151;
  --text-muted: #6b7280;
  --border: #e2e8f0;
  --border-strong: #cbd5e1;

  --primary: #2563eb;
  --primary-hover: #1d4ed8;
  --primary-soft: #eff6ff;
  --primary-border: #bfdbfe;

  --success: #15803d;
  --success-bg: #f0fdf4;
  --success-border: #bbf7d0;

  --warning: #b45309;
  --warning-bg: #fffbeb;
  --warning-border: #fde68a;

  --danger: #b91c1c;
  --danger-bg: #fef2f2;
  --danger-border: #fecaca;

  /* Crisp Textbook SVG Colors */
  --svg-stroke: #1e293b;
  --svg-accent: #2563eb;
  --svg-warn: #d97706;
  --svg-good: #16a34a;
  --svg-bad: #dc2626;

  --shadow-sm: 0 1px 3px rgba(15, 23, 42, 0.05);
  --radius: 10px;
  --sidebar-w: 276px;
}

body.dark-mode {
  /* Calm Matte Dark Theme (No neon, easy on eyes) */
  --bg: #121417;
  --bg-sidebar: #171a1e;
  --bg-card: #1b1f24;
  --bg-soft: #22272e;
  --bg-hover: #282e37;
  --text: #f3f4f6;
  --text-secondary: #d1d5db;
  --text-muted: #9ca3af;
  --border: #2d333b;
  --border-strong: #3d444d;

  --primary: #60a5fa;
  --primary-hover: #3b82f6;
  --primary-soft: rgba(96, 165, 250, 0.12);
  --primary-border: rgba(96, 165, 250, 0.3);

  --success: #4ade80;
  --success-bg: rgba(74, 222, 128, 0.1);
  --success-border: rgba(74, 222, 128, 0.28);

  --warning: #fbbf24;
  --warning-bg: rgba(251, 191, 36, 0.1);
  --warning-border: rgba(251, 191, 36, 0.28);

  --danger: #f87171;
  --danger-bg: rgba(248, 113, 113, 0.1);
  --danger-border: rgba(248, 113, 113, 0.28);

  --svg-stroke: #e5e7eb;
  --svg-accent: #60a5fa;
  --svg-warn: #fbbf24;
  --svg-good: #4ade80;
  --svg-bad: #f87171;

  --shadow-sm: 0 1px 3px rgba(0, 0, 0, 0.25);
}

* {
  box-sizing: border-box;
  margin: 0;
  padding: 0;
}

body {
  font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Inter, Roboto, sans-serif;
  background: var(--bg);
  color: var(--text);
  line-height: 1.65;
  font-size: 15px;
  min-height: 100vh;
}

/* ==================== LEFT COLLAPSIBLE SIDEBAR ==================== */
.left-sidebar {
  position: fixed;
  top: 0;
  left: 0;
  bottom: 0;
  width: var(--sidebar-w);
  background: var(--bg-sidebar);
  border-right: 1px solid var(--border);
  display: flex;
  flex-direction: column;
  z-index: 200;
  transition: transform 0.22s ease;
}

body.sidebar-collapsed .left-sidebar {
  transform: translateX(-100%);
}

.sidebar-top {
  padding: 16px 16px 14px;
  border-bottom: 1px solid var(--border);
}

.sidebar-brand-row {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 8px;
}

.brand {
  display: flex;
  align-items: center;
  gap: 10px;
  cursor: pointer;
}

.brand-icon {
  width: 32px;
  height: 32px;
  border-radius: 8px;
  background: var(--primary);
  color: #ffffff;
  display: flex;
  align-items: center;
  justify-content: center;
  font-size: 16px;
  font-weight: 700;
  flex-shrink: 0;
}

body.dark-mode .brand-icon {
  color: #0f172a;
}

.brand-text h1 {
  font-size: 0.98rem;
  font-weight: 700;
  color: var(--text);
  line-height: 1.2;
}

.brand-text span {
  font-size: 0.75rem;
  color: var(--text-muted);
}

.collapse-btn {
  background: transparent;
  color: var(--text-muted);
  border: 1px solid var(--border);
  border-radius: 7px;
  width: 30px;
  height: 30px;
  cursor: pointer;
  display: inline-flex;
  align-items: center;
  justify-content: center;
  font-size: 0.85rem;
  transition: background 0.15s, color 0.15s;
}

.collapse-btn:hover {
  background: var(--bg-hover);
  color: var(--text);
}

.sidebar-progress {
  margin-top: 12px;
  background: var(--bg-soft);
  border: 1px solid var(--border);
  border-radius: 8px;
  padding: 8px 10px;
}

.sidebar-progress-row {
  display: flex;
  justify-content: space-between;
  font-size: 0.78rem;
  color: var(--text-secondary);
  font-weight: 600;
  margin-bottom: 5px;
}

.sidebar-progress-row strong {
  color: var(--primary);
}

/* Sidebar Navigation Links */
.sidebar-nav {
  flex: 1;
  overflow-y: auto;
  padding: 12px 10px;
}

.sidebar-section-label {
  font-size: 0.7rem;
  font-weight: 700;
  text-transform: uppercase;
  letter-spacing: 0.05em;
  color: var(--text-muted);
  padding: 6px 10px 6px;
}

.nav-tab {
  width: 100%;
  background: transparent;
  color: var(--text-secondary);
  border: none;
  border-radius: 8px;
  padding: 9px 11px;
  margin-bottom: 3px;
  font-size: 0.89rem;
  font-weight: 600;
  cursor: pointer;
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 8px;
  text-align: left;
  transition: background 0.14s, color 0.14s;
}

.nav-tab-left {
  display: flex;
  align-items: center;
  gap: 9px;
}

.nav-tab:hover {
  background: var(--bg-hover);
  color: var(--text);
}

.nav-tab.active {
  background: var(--primary-soft);
  color: var(--primary);
  font-weight: 700;
}

.tab-badge {
  font-size: 0.72rem;
  padding: 1px 7px;
  border-radius: 99px;
  background: var(--bg-soft);
  border: 1px solid var(--border);
  color: var(--text-muted);
  font-weight: 600;
}

.nav-tab.active .tab-badge {
  background: var(--primary);
  border-color: var(--primary);
  color: #ffffff;
}

body.dark-mode .nav-tab.active .tab-badge {
  color: #0f172a;
}

/* Sub-navigation for the 7 Note Modules inside Left Sidebar */
.sidebar-subnav {
  margin: 2px 0 8px 14px;
  padding-left: 10px;
  border-left: 2px solid var(--border);
  display: none;
}

.sidebar-subnav.open {
  display: block;
}

.subnav-btn {
  width: 100%;
  text-align: left;
  background: transparent;
  color: var(--text-muted);
  border: none;
  border-radius: 6px;
  padding: 6px 9px;
  margin-bottom: 2px;
  cursor: pointer;
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 6px;
  font-size: 0.81rem;
  font-weight: 500;
  transition: background 0.14s, color 0.14s;
}

.subnav-btn:hover {
  background: var(--bg-hover);
  color: var(--text);
}

.subnav-btn.active {
  background: var(--primary-soft);
  color: var(--primary);
  font-weight: 700;
}

.subnav-check {
  font-size: 0.76rem;
  flex-shrink: 0;
}

/* Sidebar Bottom Controls */
.sidebar-footer {
  padding: 12px;
  border-top: 1px solid var(--border);
  display: flex;
  gap: 8px;
}

.sidebar-footer .icon-btn {
  flex: 1;
  text-align: center;
  justify-content: center;
}

.icon-btn {
  display: inline-flex;
  align-items: center;
  gap: 6px;
  background: var(--bg-soft);
  color: var(--text-secondary);
  border: 1px solid var(--border);
  border-radius: 8px;
  padding: 7px 10px;
  cursor: pointer;
  font-size: 0.81rem;
  font-weight: 600;
  transition: background 0.15s, border-color 0.15s;
}

.icon-btn:hover {
  background: var(--bg-hover);
  border-color: var(--border-strong);
  color: var(--text);
}

/* Floating Re-open Sidebar Button */
.open-sidebar-fab {
  position: fixed;
  top: 14px;
  left: 14px;
  z-index: 150;
  background: var(--bg-card);
  color: var(--text);
  border: 1px solid var(--border-strong);
  border-radius: 8px;
  padding: 8px 12px;
  font-size: 0.85rem;
  font-weight: 600;
  cursor: pointer;
  box-shadow: var(--shadow-sm);
  display: none;
  align-items: center;
  gap: 6px;
}

.open-sidebar-fab:hover {
  background: var(--bg-hover);
}

body.sidebar-collapsed .open-sidebar-fab {
  display: inline-flex;
}

.sidebar-overlay {
  display: none;
  position: fixed;
  inset: 0;
  background: rgba(15, 23, 42, 0.4);
  z-index: 190;
}

/* ==================== MAIN CONTENT AREA ==================== */
.main-area {
  margin-left: var(--sidebar-w);
  min-height: 100vh;
  transition: margin-left 0.22s ease;
}

body.sidebar-collapsed .main-area {
  margin-left: 0;
}

.container {
  max-width: 920px;
  margin: 0 auto;
  padding: 32px 28px 80px;
}

body.sidebar-collapsed .container {
  padding-top: 56px;
}

@media (max-width: 900px) {
  .left-sidebar {
    transform: translateX(-100%);
  }
  body.mobile-sidebar-open .left-sidebar {
    transform: translateX(0);
  }
  body.mobile-sidebar-open .sidebar-overlay {
    display: block;
  }
  .main-area {
    margin-left: 0;
  }
  .open-sidebar-fab {
    display: inline-flex;
  }
  .container {
    padding: 58px 16px 64px;
  }
}

.view-section {
  display: none;
}

.view-section.active {
  display: block;
}

/* ==================== CLEAN CARDS, TYPOGRAPHY & BUTTONS ==================== */
.page-header {
  margin-bottom: 20px;
}

.page-header h2 {
  font-size: 1.45rem;
  font-weight: 700;
  color: var(--text);
  margin-bottom: 6px;
}

.page-header p {
  color: var(--text-muted);
  font-size: 0.94rem;
}

.hero-banner {
  background: var(--bg-card);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 22px 24px;
  margin-bottom: 18px;
  box-shadow: var(--shadow-sm);
}

.hero-banner h2 {
  font-size: 1.32rem;
  font-weight: 700;
  margin-bottom: 6px;
}

.hero-banner p {
  color: var(--text-secondary);
  font-size: 0.94rem;
  margin-bottom: 16px;
}

.quick-start-btns {
  display: flex;
  gap: 8px;
  flex-wrap: wrap;
}

.btn {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  gap: 7px;
  padding: 9px 15px;
  border-radius: 8px;
  font-weight: 600;
  font-size: 0.88rem;
  cursor: pointer;
  border: 1px solid transparent;
  transition: background 0.15s, border-color 0.15s;
}

.btn-primary {
  background: var(--primary);
  color: #ffffff;
}

body.dark-mode .btn-primary {
  color: #0f172a;
}

.btn-primary:hover {
  background: var(--primary-hover);
}

.btn-secondary {
  background: var(--bg-soft);
  color: var(--text);
  border-color: var(--border-strong);
}

.btn-secondary:hover {
  background: var(--bg-hover);
}

.btn-success {
  background: var(--success);
  color: #ffffff;
}

body.dark-mode .btn-success {
  color: #0f172a;
}

.btn-warning {
  background: var(--warning-bg);
  color: var(--warning);
  border-color: var(--warning-border);
}

.btn-danger {
  background: var(--danger-bg);
  color: var(--danger);
  border-color: var(--danger-border);
}

.btn-sm {
  padding: 6px 11px;
  font-size: 0.8rem;
}

/* Progress Cards */
.stats-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(195px, 1fr));
  gap: 12px;
  margin-bottom: 20px;
}

.stat-card {
  background: var(--bg-card);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 15px 16px;
  box-shadow: var(--shadow-sm);
  cursor: pointer;
  transition: border-color 0.15s;
}

.stat-card:hover {
  border-color: var(--primary);
}

.stat-card .stat-title {
  font-size: 0.8rem;
  color: var(--text-muted);
  font-weight: 600;
  margin-bottom: 4px;
}

.stat-card .stat-value {
  font-size: 1.35rem;
  font-weight: 700;
  color: var(--text);
}

.progress-track {
  height: 6px;
  background: var(--bg-soft);
  border: 1px solid var(--border);
  border-radius: 99px;
  margin-top: 8px;
  overflow: hidden;
}

.progress-fill {
  height: 100%;
  background: var(--primary);
  border-radius: 99px;
  transition: width 0.25s ease;
}

/* Cards & Grids */
.grid-2 {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(320px, 1fr));
  gap: 14px;
  margin-bottom: 16px;
}

.card {
  background: var(--bg-card);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 22px 24px;
  box-shadow: var(--shadow-sm);
  margin-bottom: 16px;
}

.card h3 {
  font-size: 1.08rem;
  font-weight: 700;
  margin-bottom: 10px;
  color: var(--text);
}

/* Formula & Callout Boxes */
.formula-box {
  background: var(--bg-soft);
  border: 1px solid var(--border);
  border-left: 3.5px solid var(--primary);
  border-radius: 8px;
  padding: 12px 15px;
  margin: 10px 0;
}

.formula-main {
  font-size: 1.05rem;
  font-weight: 700;
  color: var(--primary);
  margin-bottom: 3px;
}

.callout {
  border-radius: 8px;
  padding: 12px 15px;
  margin: 12px 0;
  font-size: 0.91rem;
  border: 1px solid transparent;
  color: var(--text);
}

.callout-tip {
  background: var(--success-bg);
  border-color: var(--success-border);
}

.callout-warn {
  background: var(--warning-bg);
  border-color: var(--warning-border);
}

.callout-exam {
  background: var(--primary-soft);
  border-color: var(--primary-border);
}

.callout-danger {
  background: var(--danger-bg);
  border-color: var(--danger-border);
}

/* Clean Tables */
.clean-table {
  width: 100%;
  border-collapse: collapse;
  margin: 12px 0;
  font-size: 0.9rem;
  border: 1px solid var(--border);
  border-radius: 8px;
  overflow: hidden;
}

.clean-table th,
.clean-table td {
  padding: 9px 12px;
  border-bottom: 1px solid var(--border);
  text-align: left;
}

.clean-table th {
  background: var(--bg-soft);
  color: var(--text);
  font-weight: 700;
  font-size: 0.84rem;
}

.clean-table tr:last-child td {
  border-bottom: none;
}

/* Note Content Typography */
.note-content h2 {
  font-size: 1.35rem;
  font-weight: 700;
  margin-bottom: 12px;
  color: var(--text);
}

.note-content h4 {
  font-size: 1.04rem;
  font-weight: 700;
  margin: 20px 0 8px;
  padding-bottom: 4px;
  border-bottom: 1px solid var(--border);
  color: var(--text);
}

.note-content p {
  color: var(--text-secondary);
  margin-bottom: 8px;
}

.note-content ul,
.note-content ol {
  padding-left: 22px;
  margin: 8px 0 12px;
  color: var(--text-secondary);
}

.note-content li {
  margin-bottom: 6px;
}

.note-content strong {
  color: var(--text);
}

/* SVG Schematic Containers */
.svg-box {
  background: var(--bg-soft);
  border: 1px solid var(--border);
  border-radius: 8px;
  padding: 14px;
  margin: 12px 0;
  text-align: center;
  overflow-x: auto;
}

.svg-box svg {
  max-width: 100%;
  height: auto;
}

.svg-caption {
  font-size: 0.8rem;
  color: var(--text-muted);
  margin-top: 6px;
}

/* Interactive Simulators */
.sim-panel {
  background: var(--bg-soft);
  border: 1px solid var(--primary-border);
  border-radius: var(--radius);
  padding: 18px;
  margin: 18px 0;
}

.sim-controls {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(185px, 1fr));
  gap: 12px;
  margin: 12px 0;
}

.sim-control label {
  display: block;
  font-size: 0.8rem;
  color: var(--text-secondary);
  margin-bottom: 4px;
  font-weight: 600;
}

.sim-control select,
.text-input {
  width: 100%;
  padding: 8px 11px;
  border-radius: 7px;
  border: 1px solid var(--border-strong);
  background: var(--bg-card);
  color: var(--text);
  font-size: 0.9rem;
}

.text-input:focus,
.sim-control select:focus {
  outline: 2px solid var(--primary);
  outline-offset: -1px;
}

.sim-control input[type="range"] {
  width: 100%;
  accent-color: var(--primary);
  margin-top: 6px;
}

.sim-readout {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(135px, 1fr));
  gap: 10px;
  margin-top: 12px;
}

.readout-item {
  background: var(--bg-card);
  border: 1px solid var(--border);
  border-radius: 8px;
  padding: 9px 10px;
  text-align: center;
}

.readout-item span {
  display: block;
  font-size: 0.75rem;
  color: var(--text-muted);
}

.readout-item strong {
  font-size: 1.02rem;
  color: var(--primary);
}

/* Notebook Thumbnails */
.notebook-thumbs {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(150px, 1fr));
  gap: 12px;
  margin-top: 12px;
}

.thumb-card {
  background: var(--bg-card);
  border: 1px solid var(--border);
  border-radius: 8px;
  overflow: hidden;
  cursor: pointer;
  transition: border-color 0.15s;
}

.thumb-card:hover {
  border-color: var(--primary);
}

.thumb-card img {
  width: 100%;
  height: 165px;
  object-fit: cover;
  display: block;
}

.thumb-card .thumb-label {
  padding: 7px 10px;
  font-size: 0.78rem;
  font-weight: 600;
  color: var(--text-secondary);
}

/* Sor Ben Bileyim (Active Recall & Flashcards) */
.mode-switch {
  display: inline-flex;
  background: var(--bg-soft);
  border: 1px solid var(--border);
  border-radius: 8px;
  padding: 3px;
  gap: 3px;
}

.mode-btn {
  background: transparent;
  color: var(--text-muted);
  border: none;
  padding: 7px 13px;
  border-radius: 6px;
  font-weight: 600;
  font-size: 0.85rem;
  cursor: pointer;
}

.mode-btn.active {
  background: var(--bg-card);
  color: var(--primary);
  box-shadow: var(--shadow-sm);
}

.overall-pill {
  background: var(--bg-soft);
  border: 1px solid var(--border);
  border-radius: 99px;
  padding: 5px 12px;
  font-size: 0.81rem;
  font-weight: 600;
}

.overall-pill strong {
  color: var(--primary);
}

.filter-bar {
  display: flex;
  gap: 6px;
  flex-wrap: wrap;
  margin-bottom: 16px;
}

.chip {
  background: var(--bg-card);
  color: var(--text-secondary);
  border: 1px solid var(--border);
  border-radius: 99px;
  padding: 5px 12px;
  font-size: 0.81rem;
  font-weight: 600;
  cursor: pointer;
}

.chip:hover {
  background: var(--bg-hover);
}

.chip.active {
  background: var(--primary-soft);
  color: var(--primary);
  border-color: var(--primary-border);
}

.flashcard-stage {
  background: var(--bg-card);
  border: 1px solid var(--border);
  border-radius: 12px;
  padding: 28px 24px;
  min-height: 250px;
  display: flex;
  flex-direction: column;
  justify-content: space-between;
  box-shadow: var(--shadow-sm);
}

.flashcard-stage.revealed {
  border-color: var(--primary-border);
}

.fc-topic {
  font-size: 0.76rem;
  text-transform: uppercase;
  letter-spacing: 0.04em;
  color: var(--primary);
  font-weight: 700;
}

.fc-question {
  font-size: 1.2rem;
  font-weight: 700;
  margin: 16px 0;
  color: var(--text);
}

.fc-answer {
  background: var(--success-bg);
  border: 1px solid var(--success-border);
  border-radius: 8px;
  padding: 14px 16px;
  margin-top: 12px;
}

.fc-answer-main {
  font-size: 1.1rem;
  font-weight: 700;
  color: var(--success);
  margin-bottom: 4px;
}

.answer-input-row {
  display: flex;
  gap: 8px;
  margin-top: 12px;
  flex-wrap: wrap;
}

.answer-input-row input {
  flex: 1;
  min-width: 200px;
}

/* Classic Problems */
.problem-card {
  background: var(--bg-card);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 20px 22px;
  margin-bottom: 14px;
  box-shadow: var(--shadow-sm);
}

.problem-header {
  display: flex;
  justify-content: space-between;
  align-items: center;
  gap: 10px;
  margin-bottom: 10px;
  flex-wrap: wrap;
}

.problem-card h3 {
  font-size: 1.06rem;
  margin-bottom: 6px;
}

.problem-card p {
  color: var(--text-secondary);
}

.badge {
  display: inline-block;
  padding: 2px 9px;
  border-radius: 99px;
  font-size: 0.74rem;
  font-weight: 600;
  border: 1px solid transparent;
}

.badge-topic {
  background: var(--primary-soft);
  color: var(--primary);
  border-color: var(--primary-border);
}

.badge-easy {
  background: var(--success-bg);
  color: var(--success);
  border-color: var(--success-border);
}

.badge-mid {
  background: var(--warning-bg);
  color: var(--warning);
  border-color: var(--warning-border);
}

.badge-hard {
  background: var(--danger-bg);
  color: var(--danger);
  border-color: var(--danger-border);
}

.solution-steps {
  background: var(--bg-soft);
  border: 1px solid var(--border);
  border-left: 3.5px solid var(--success);
  border-radius: 8px;
  padding: 14px 16px;
  margin-top: 12px;
}

.solution-steps ol {
  padding-left: 20px;
}

.solution-steps li {
  margin-bottom: 6px;
}

/* Multiple Choice Quiz */
.quiz-question-card {
  background: var(--bg-card);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 20px 22px;
  margin-bottom: 14px;
  box-shadow: var(--shadow-sm);
}

.options-list {
  display: grid;
  gap: 8px;
  margin-top: 12px;
}

.option-btn {
  width: 100%;
  text-align: left;
  background: var(--bg-soft);
  color: var(--text);
  border: 1px solid var(--border);
  border-radius: 8px;
  padding: 11px 14px;
  font-size: 0.92rem;
  font-weight: 500;
  cursor: pointer;
  display: flex;
  align-items: center;
  gap: 11px;
  transition: background 0.12s, border-color 0.12s;
}

.option-btn:hover:not(:disabled) {
  border-color: var(--primary);
  background: var(--primary-soft);
}

.option-letter {
  width: 26px;
  height: 26px;
  border-radius: 6px;
  background: var(--bg-card);
  border: 1px solid var(--border-strong);
  display: inline-flex;
  align-items: center;
  justify-content: center;
  font-weight: 700;
  font-size: 0.8rem;
  flex-shrink: 0;
}

.option-btn.selected {
  border-color: var(--primary);
  background: var(--primary-soft);
}

.option-btn.correct {
  border-color: var(--success);
  background: var(--success-bg);
}

.option-btn.correct .option-letter {
  background: var(--success);
  color: #ffffff;
  border-color: var(--success);
}

.option-btn.wrong {
  border-color: var(--danger);
  background: var(--danger-bg);
}

.option-btn.wrong .option-letter {
  background: var(--danger);
  color: #ffffff;
  border-color: var(--danger);
}

.quiz-explanation {
  margin-top: 12px;
  padding: 11px 14px;
  border-radius: 8px;
  background: var(--bg-soft);
  border: 1px solid var(--border);
  border-left: 3.5px solid var(--primary);
  font-size: 0.89rem;
  color: var(--text-secondary);
}

/* Modal for Image Zoom */
.modal-backdrop {
  position: fixed;
  inset: 0;
  background: rgba(15, 23, 42, 0.78);
  z-index: 999;
  display: none;
  align-items: center;
  justify-content: center;
  padding: 18px;
}

.modal-backdrop.open {
  display: flex;
}

.modal-content {
  background: var(--bg-card);
  border: 1px solid var(--border);
  border-radius: 12px;
  max-width: 880px;
  width: 100%;
  max-height: 92vh;
  display: flex;
  flex-direction: column;
  overflow: hidden;
}

.modal-header {
  padding: 12px 16px;
  border-bottom: 1px solid var(--border);
  display: flex;
  justify-content: space-between;
  align-items: center;
  gap: 10px;
  flex-wrap: wrap;
}

.modal-body {
  padding: 14px;
  overflow: auto;
  text-align: center;
  background: var(--bg-soft);
}

.modal-body img {
  max-width: 100%;
  height: auto;
  border-radius: 6px;
}

.kbd {
  background: var(--bg-card);
  border: 1px solid var(--border-strong);
  border-radius: 5px;
  padding: 1px 6px;
  font-size: 0.74rem;
  font-family: monospace;
}

/* ==================== COURSE / CATEGORY SWITCHER ==================== */
.course-switcher {
  margin-top: 12px;
  display: flex;
  flex-direction: column;
  gap: 6px;
}

.course-switcher-label {
  font-size: 0.69rem;
  font-weight: 700;
  text-transform: uppercase;
  letter-spacing: 0.05em;
  color: var(--text-muted);
}

.course-btn {
  width: 100%;
  display: flex;
  align-items: center;
  gap: 9px;
  padding: 8px 10px;
  border-radius: 8px;
  border: 1px solid var(--border);
  background: var(--bg-soft);
  color: var(--text-secondary);
  cursor: pointer;
  text-align: left;
  transition: all 0.15s ease;
}

.course-btn:hover {
  background: var(--bg-hover);
  border-color: var(--border-strong);
  color: var(--text);
}

.course-btn.active {
  background: var(--primary-soft);
  border-color: var(--primary);
  color: var(--primary);
  box-shadow: 0 1px 2px rgba(37, 99, 235, 0.08);
}

.course-btn-icon {
  font-size: 1.1rem;
  flex-shrink: 0;
}

.course-btn-info {
  display: flex;
  flex-direction: column;
  line-height: 1.22;
}

.course-btn-title {
  font-size: 0.82rem;
  font-weight: 700;
}

.course-btn-sub {
  font-size: 0.7rem;
  color: var(--text-muted);
}

.course-btn.active .course-btn-sub {
  color: var(--primary);
  opacity: 0.85;
}