:root {
    --bg-primary: #0a0c10;
    --bg-secondary: #12161d;
    --bg-tertiary: #1a1e28;
    --bg-elevated: #222834;
    --border: #2a3140;
    --border-light: #3a4255;
    --text-primary: #f0f2f5;
    --text-secondary: #9ca3af;
    --text-muted: #6b7280;
    --accent: #3b82f6;
    --accent-hover: #60a5fa;
    --accent-glow: rgba(b82f659, 130, 246, 0.15);
    --success: #10b981;
    --warning: #f59e0b;
    --purple: #8b5cf6;
    --pink: #ec4899;
  }

  [data-theme="light"] {
    --bg-primary: #f8fafc;
    --bg-secondary: #ffffff;
    --bg-tertiary: #f1f5f9;
    --bg-elevated: #ffffff;
    --border: #e2e8f0;
    --border-light: #cbd5e1;
    --text-primary: #0f172a;
    --text-secondary: #475569;
    --text-muted: #94a3b8;
    --accent-glow: rgba(59, 130, 246, 0.1);
  }

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

  body {
    background: var(--bg-primary);
    color: var(--text-primary);
    font-family: 'Inter', -apple-system, BlinkMacSystemFont, sans-serif;
    min-height: 100vh;
    padding: 0;
    line-height: 1.6;
    overflow-x: hidden;
  }

  body::before {
    content: '';
    position: fixed;
    top: 0;
    left: 0;
    right: 0;
    bottom: 0;
    background: 
      radial-gradient(ellipse 80% 50% at 20% -10%, rgba(59, 130, 246, 0.08), transparent),
      radial-gradient(ellipse 60% 40% at 80% 100%, rgba(139, 92, 246, 0.06), transparent);
    pointer-events: none;
    z-index: 0;
  }

  [data-theme="light"] body::before {
    background: 
      radial-gradient(ellipse 80% 50% at 20% -10%, rgba(59, 130, 246, 0.05), transparent),
      radial-gradient(ellipse 60% 40% at 80% 100%, rgba(139, 92, 246, 0.03), transparent);
  }

  .container {
    max-width: 1280px;
    margin: 0 auto;
    padding: 0 48px;
    position: relative;
    z-index: 1;
  }

  /* Header */
  header {
    padding: 48px 0 40px;
    border-bottom: 1px solid var(--border);
    margin-bottom: 48px;
  }

  .header-top {
    display: flex;
    justify-content: space-between;
    align-items: flex-start;
    margin-bottom: 32px;
  }

  .brand {
    display: flex;
    flex-direction: column;
    gap: 6px;
  }

  .breadcrumb {
    font-size: 0.7rem;
    font-weight: 500;
    color: var(--text-muted);
    text-transform: uppercase;
    letter-spacing: 0.12em;
  }

  h1 {
    font-size: 2.25rem;
    font-weight: 700;
    color: var(--text-primary);
    letter-spacing: -0.03em;
    background: linear-gradient(135deg, var(--text-primary) 0%, var(--accent-hover) 100%);
    -webkit-background-clip: text;
    -webkit-text-fill-color: transparent;
    background-clip: text;
  }

  [data-theme="light"] h1 {
    background: none;
    -webkit-text-fill-color: var(--text-primary);
  }

  .header-content {
    display: flex;
    justify-content: space-between;
    align-items: flex-end;
    gap: 32px;
  }

  .subtitle {
    color: var(--text-secondary);
    font-size: 1rem;
    max-width: 520px;
    line-height: 1.7;
  }

  .stats-row {
    display: flex;
    gap: 32px;
  }

  .stat {
    display: flex;
    flex-direction: column;
    align-items: center;
    gap: 4px;
    padding: 16px 24px;
    background: var(--bg-secondary);
    border: 1px solid var(--border);
    border-radius: 12px;
    min-width: 90px;
  }

  .stat-value {
    font-size: 1.5rem;
    font-weight: 700;
    color: var(--accent);
    letter-spacing: -0.02em;
  }

  .stat-label {
    font-size: 0.7rem;
    font-weight: 500;
    color: var(--text-muted);
    text-transform: uppercase;
    letter-spacing: 0.08em;
  }

  /* Theme Toggle */
  .theme-toggle {
    position: fixed;
    top: 24px;
    right: 24px;
    background: var(--bg-secondary);
    border: 1px solid var(--border);
    border-radius: 14px;
    padding: 10px 18px;
    cursor: pointer;
    display: flex;
    align-items: center;
    gap: 8px;
    font-size: 0.85rem;
    font-weight: 500;
    color: var(--text-secondary);
    transition: all 0.25s ease;
    z-index: 100;
  }

  .theme-toggle:hover {
    background: var(--bg-tertiary);
    border-color: var(--border-light);
    color: var(--text-primary);
    transform: translateY(-2px);
  }

  .theme-icon {
    font-size: 1rem;
  }

  /* Section */
  .section-header {
    display: flex;
    justify-content: space-between;
    align-items: center;
    margin-bottom: 24px;
  }

  .section-title {
    font-size: 0.65rem;
    font-weight: 600;
    color: var(--text-muted);
    text-transform: uppercase;
    letter-spacing: 0.12em;
  }

  .section-count {
    font-size: 0.75rem;
    color: var(--text-muted);
    background: var(--bg-tertiary);
    padding: 6px 14px;
    border-radius: 20px;
  }

  /* Course Grid */
  .courses-grid {
    display: grid;
    grid-template-columns: repeat(3, 1fr);
    gap: 20px;
    margin-bottom: 64px;
  }

  .course-card {
    background: var(--bg-secondary);
    border: 1px solid var(--border);
    border-radius: 16px;
    overflow: hidden;
    cursor: pointer;
    transition: all 0.3s cubic-bezier(0.4, 0, 0.2, 1);
    position: relative;
  }

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

  .course-card:hover {
    border-color: var(--border-light);
    transform: translateY(-6px);
    box-shadow: 0 20px 40px rgba(0, 0, 0, 0.3);
  }

  .course-card:hover::before {
    opacity: 1;
  }

  .course-card[data-course="cse411"] { --card-accent: var(--accent); }
  .course-card[data-course="cse412"] { --card-accent: var(--accent); }
  .course-card[data-course="cse415"] { --card-accent: var(--success); }
  .course-card[data-course="ged411"] { --card-accent: var(--warning); }
  .course-card[data-course="cse401"] { --card-accent: var(--purple); }
  .course-card[data-course="cse413"] { --card-accent: var(--pink); }
  .course-card[data-course="cse414"] { --card-accent: var(--success); }

  .card-header {
    padding: 24px 24px 16px;
    border-bottom: 1px solid var(--border);
  }

  .card-header-top {
    display: flex;
    justify-content: space-between;
    align-items: center;
    margin-bottom: 12px;
  }

  .course-code {
    font-size: 0.7rem;
    font-weight: 700;
    letter-spacing: 0.05em;
    background: var(--bg-tertiary);
    color: var(--text-secondary);
    padding: 6px 12px;
    border-radius: 6px;
  }

  .credit-badge {
    font-size: 0.65rem;
    font-weight: 600;
    color: var(--text-muted);
    padding: 4px 10px;
    background: var(--bg-tertiary);
    border-radius: 16px;
  }

  .course-title {
    font-size: 1.1rem;
    font-weight: 600;
    color: var(--text-primary);
    line-height: 1.4;
  }

  .card-body {
    padding: 20px 24px 24px;
  }

  .card-preview {
    display: flex;
    flex-wrap: wrap;
    gap: 8px;
  }

  .preview-item {
    font-size: 0.7rem;
    font-weight: 500;
    color: var(--text-muted);
    background: var(--bg-tertiary);
    padding: 6px 12px;
    border-radius: 6px;
    display: flex;
    align-items: center;
    gap: 6px;
  }

  .preview-item::before {
    content: '';
    width: 4px;
    height: 4px;
    background: var(--accent);
    border-radius: 50%;
  }

  /* Footer */
  footer {
    padding: 32px 0;
    border-top: 1px solid var(--border);
    text-align: center;
    color: var(--text-muted);
    font-size: 0.8rem;
  }

  footer a {
    color: var(--accent);
    text-decoration: none;
  }

  footer a:hover {
    text-decoration: underline;
  }

  /* Modal */
  .modal-overlay {
    position: fixed;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
    background: rgba(0, 0, 0, 0.7);
    backdrop-filter: blur(8px);
    display: flex;
    align-items: center;
    justify-content: center;
    z-index: 1000;
    opacity: 0;
    visibility: hidden;
    transition: all 0.3s ease;
    padding: 24px;
  }

  [data-theme="light"] .modal-overlay {
    background: rgba(0, 0, 0, 0.5);
  }

  .modal-overlay.active {
    opacity: 1;
    visibility: visible;
  }

  .modal {
    background: var(--bg-secondary);
    border: 1px solid var(--border);
    border-radius: 20px;
    width: 100%;
    max-width: 720px;
    max-height: 85vh;
    overflow-y: auto;
    transform: scale(0.95) translateY(20px);
    transition: transform 0.3s ease;
  }

  .modal-overlay.active .modal {
    transform: scale(1) translateY(0);
  }

  .modal-close {
    position: absolute;
    top: 20px;
    right: 20px;
    background: var(--bg-tertiary);
    border: 1px solid var(--border);
    color: var(--text-secondary);
    width: 40px;
    height: 40px;
    border-radius: 50%;
    font-size: 1.5rem;
    cursor: pointer;
    display: flex;
    align-items: center;
    justify-content: center;
    transition: all 0.2s ease;
    z-index: 10;
  }

  .modal-close:hover {
    background: var(--border);
    color: var(--text-primary);
    transform: rotate(90deg);
  }

  .modal-header {
    padding: 32px 32px 24px;
    border-bottom: 1px solid var(--border);
    display: flex;
    align-items: center;
    gap: 16px;
    flex-wrap: wrap;
    position: relative;
  }

  .modal-code {
    font-size: 0.75rem;
    font-weight: 700;
    letter-spacing: 0.05em;
    background: var(--bg-tertiary);
    color: var(--text-secondary);
    padding: 8px 14px;
    border-radius: 8px;
  }

  .modal-title {
    font-size: 1.35rem;
    font-weight: 700;
    flex: 1;
    letter-spacing: -0.01em;
  }

  .modal-credit {
    font-size: 0.75rem;
    font-weight: 600;
    color: var(--text-muted);
    padding: 6px 14px;
    background: var(--bg-tertiary);
    border-radius: 20px;
  }

  .modal-body {
    padding: 28px 32px 32px;
  }

  .resource-group {
    margin-bottom: 28px;
  }

  .resource-group:last-of-type {
    margin-bottom: 0;
  }

  .group-label {
    font-size: 0.65rem;
    font-weight: 600;
    color: var(--text-muted);
    text-transform: uppercase;
    letter-spacing: 0.1em;
    margin-bottom: 14px;
    display: flex;
    align-items: center;
    gap: 10px;
  }

  .group-label::after {
    content: '';
    flex: 1;
    height: 1px;
    background: var(--border);
  }

  .resource-list {
    display: flex;
    flex-direction: column;
    gap: 10px;
  }

  .resource-link {
    display: flex;
    align-items: center;
    gap: 16px;
    padding: 16px 20px;
    background: var(--bg-tertiary);
    border: 1px solid transparent;
    border-radius: 12px;
    text-decoration: none;
    color: var(--text-secondary);
    font-size: 0.9rem;
    transition: all 0.2s ease;
  }

  .resource-link:hover {
    background: var(--bg-elevated);
    border-color: var(--border);
    color: var(--text-primary);
    transform: translateX(8px);
  }

  .resource-link .icon {
    width: 36px;
    height: 36px;
    display: flex;
    align-items: center;
    justify-content: center;
    font-size: 1rem;
    background: var(--bg-secondary);
    border-radius: 10px;
    flex-shrink: 0;
  }

  .resource-link .name {
    flex: 1;
    font-weight: 500;
  }

  .resource-link .type {
    font-size: 0.65rem;
    font-weight: 600;
    color: var(--text-muted);
    text-transform: uppercase;
    letter-spacing: 0.06em;
    padding: 5px 12px;
    background: var(--bg-secondary);
    border-radius: 6px;
  }

  .tip-box {
    margin-top: 28px;
    padding: 20px 24px;
    background: var(--accent-glow);
    border: 1px solid rgba(59, 130, 246, 0.2);
    border-radius: 12px;
    font-size: 0.9rem;
    color: var(--text-secondary);
    line-height: 1.7;
    display: flex;
    gap: 12px;
  }

  .tip-box::before {
    content: '💡';
    font-size: 1.1rem;
    flex-shrink: 0;
  }

  .tip-box strong {
    color: var(--accent-hover);
    font-weight: 600;
  }

  /* Subscribe Modal */
  .subscribe-modal {
    max-width: 420px;
    text-align: center;
  }

  .subscribe-modal-content {
    padding: 48px 32px;
  }

  .subscribe-icon {
    font-size: 2.5rem;
    margin-bottom: 16px;
  }

  .subscribe-title {
    font-size: 1.5rem;
    font-weight: 700;
    margin-bottom: 8px;
    letter-spacing: -0.01em;
  }

  .subscribe-desc {
    color: var(--text-secondary);
    font-size: 0.9rem;
    margin-bottom: 24px;
    line-height: 1.6;
  }

  .subscribe-form {
    display: flex;
    flex-direction: column;
    gap: 12px;
  }

  .subscribe-input {
    padding: 14px 18px;
    background: var(--bg-tertiary);
    border: 1px solid var(--border);
    border-radius: 12px;
    font-size: 0.9rem;
    color: var(--text-primary);
    outline: none;
    transition: all 0.2s ease;
  }

  .subscribe-input::placeholder {
    color: var(--text-muted);
  }

  .subscribe-input:focus {
    border-color: var(--accent);
    box-shadow: 0 0 0 3px var(--accent-glow);
  }

  .subscribe-btn {
    padding: 14px 24px;
    background: var(--accent);
    border: none;
    border-radius: 12px;
    font-size: 0.9rem;
    font-weight: 600;
    color: white;
    cursor: pointer;
    transition: all 0.2s ease;
  }

  .subscribe-btn:hover {
    background: var(--accent-hover);
    transform: translateY(-2px);
  }

  .subscribe-success {
    display: none;
    color: var(--success);
    font-size: 0.9rem;
    font-weight: 500;
    margin-top: 16px;
  }

  .subscribe-success.show {
    display: block;
  }

  /* Responsive */
  @media (max-width: 1100px) {
    .courses-grid { grid-template-columns: repeat(2, 1fr); }
  }

  @media (max-width: 768px) {
    .container { padding: 0 24px; }
    .header-content { flex-direction: column; align-items: flex-start; gap: 24px; }
    .header-top { flex-direction: column; gap: 20px; }
    .stats-row { width: 100%; justify-content: space-between; }
    .courses-grid { grid-template-columns: 1fr; }
    h1 { font-size: 1.75rem; }
    .theme-toggle { top: 16px; right: 16px; padding: 8px 14px; }
  }