:root {
    --bg: #080c10;
    --bg2: #0d1117;
    --bg3: #131920;
    --bg4: #1a2230;
    --border: #1f2d3d;
    --border2: #243447;
    --accent: #00e5a0;
    --accent2: #00bfff;
    --accent3: #7c6af7;
    --text: #cdd9e5;
    --text2: #8b9daf;
    --text3: #5a6d7e;
    --glow: rgba(0,229,160,0.12);
    --glow2: rgba(0,191,255,0.1);
  }

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

  html { scroll-behavior: smooth; }

  body {
    background: var(--bg);
    color: var(--text);
    font-family: 'Syne', sans-serif;
    min-height: 100vh;
    overflow-x: hidden;
  }

  /* Grid background */
  body::before {
    content: '';
    position: fixed;
    inset: 0;
    background-image:
      linear-gradient(rgba(0,229,160,0.025) 1px, transparent 1px),
      linear-gradient(90deg, rgba(0,229,160,0.025) 1px, transparent 1px);
    background-size: 60px 60px;
    pointer-events: none;
    z-index: 0;
  }

  /* ===== HEADER ===== */
  header {
    position: sticky;
    top: 0;
    z-index: 100;
    background: rgba(8,12,16,0.92);
    backdrop-filter: blur(20px);
    border-bottom: 1px solid var(--border);
    padding: 0 40px;
  }

  nav {
    max-width: 1400px;
    margin: 0 auto;
    display: flex;
    align-items: center;
    gap: 32px;
    height: 64px;
  }

  .logo {
    font-family: 'Space Mono', monospace;
    font-weight: 700;
    font-size: 18px;
    letter-spacing: -0.5px;
    flex-shrink: 0;
  }

  .logo span:first-child { color: var(--accent); }
  .logo span:last-child { color: var(--text2); }

  .search-wrap {
    flex: 1;
    max-width: 480px;
    position: relative;
  }

  .search-wrap svg {
    position: absolute;
    left: 14px;
    top: 50%;
    transform: translateY(-50%);
    color: var(--text3);
    pointer-events: none;
  }

  #search {
    width: 100%;
    background: var(--bg3);
    border: 1px solid var(--border);
    border-radius: 8px;
    padding: 9px 14px 9px 40px;
    color: var(--text);
    font-family: 'Inter', sans-serif;
    font-size: 14px;
    transition: border-color 0.2s, box-shadow 0.2s;
    outline: none;
  }

  #search:focus {
    border-color: var(--accent);
    box-shadow: 0 0 0 3px var(--glow);
  }

  #search::placeholder { color: var(--text3); }

  .nav-tags {
    display: flex;
    gap: 8px;
    flex-wrap: nowrap;
    overflow: hidden;
    margin-left: auto;
  }

  .nav-tag {
    font-family: 'Space Mono', monospace;
    font-size: 11px;
    padding: 4px 10px;
    border-radius: 4px;
    border: 1px solid var(--border2);
    color: var(--text3);
    cursor: pointer;
    white-space: nowrap;
    transition: all 0.2s;
    background: transparent;
  }

  .nav-tag:hover, .nav-tag.active {
    border-color: var(--accent);
    color: var(--accent);
    background: var(--glow);
  }

  /* ===== HERO ===== */
  .hero {
    position: relative;
    z-index: 1;
    max-width: 1400px;
    margin: 0 auto;
    padding: 72px 40px 48px;
    display: flex;
    flex-direction: column;
    gap: 16px;
  }

  .hero-tag {
    font-family: 'Space Mono', monospace;
    font-size: 11px;
    color: var(--accent);
    letter-spacing: 3px;
    text-transform: uppercase;
  }

  .hero h1 {
    font-size: clamp(36px, 5vw, 64px);
    font-weight: 800;
    line-height: 1.05;
    letter-spacing: -2px;
    color: #fff;
  }

  .hero h1 em {
    font-style: normal;
    background: linear-gradient(135deg, var(--accent), var(--accent2));
    -webkit-background-clip: text;
    -webkit-text-fill-color: transparent;
    background-clip: text;
  }

  .hero p {
    font-family: 'Inter', sans-serif;
    font-size: 16px;
    font-weight: 300;
    color: var(--text2);
    max-width: 540px;
    line-height: 1.7;
  }

  .hero-stats {
    display: flex;
    gap: 32px;
    margin-top: 8px;
  }

  .stat {
    display: flex;
    flex-direction: column;
    gap: 2px;
  }

  .stat-num {
    font-family: 'Space Mono', monospace;
    font-size: 22px;
    font-weight: 700;
    color: var(--accent);
  }

  .stat-label {
    font-family: 'Inter', sans-serif;
    font-size: 12px;
    color: var(--text3);
    text-transform: uppercase;
    letter-spacing: 1px;
  }

  /* ===== MAIN LAYOUT ===== */
  .container {
    position: relative;
    z-index: 1;
    max-width: 1400px;
    margin: 0 auto;
    padding: 0 40px 80px;
  }

  /* Category filter bar */
  .filter-bar {
    display: flex;
    gap: 8px;
    flex-wrap: wrap;
    padding: 20px 0 32px;
    border-bottom: 1px solid var(--border);
    margin-bottom: 40px;
  }

  .filter-btn {
    display: flex;
    align-items: center;
    gap: 6px;
    padding: 6px 14px;
    border-radius: 6px;
    border: 1px solid var(--border);
    background: transparent;
    color: var(--text2);
    font-family: 'Syne', sans-serif;
    font-size: 13px;
    font-weight: 600;
    cursor: pointer;
    transition: all 0.2s;
  }

  .filter-btn .dot {
    width: 6px;
    height: 6px;
    border-radius: 50%;
    background: var(--accent);
    opacity: 0.4;
    transition: opacity 0.2s;
  }

  .filter-btn:hover, .filter-btn.active {
    border-color: var(--accent);
    color: var(--accent);
    background: var(--glow);
  }

  .filter-btn.active .dot { opacity: 1; }

  /* ===== CATEGORY SECTIONS ===== */
  .section {
    margin-bottom: 48px;
    animation: fadeIn 0.4s ease;
  }

  @keyframes fadeIn {
    from { opacity: 0; transform: translateY(12px); }
    to { opacity: 1; transform: translateY(0); }
  }

  .section-header {
    display: flex;
    align-items: center;
    gap: 16px;
    margin-bottom: 20px;
    cursor: pointer;
    user-select: none;
  }

  .section-icon {
    width: 40px;
    height: 40px;
    border-radius: 10px;
    display: flex;
    align-items: center;
    justify-content: center;
    font-size: 18px;
    flex-shrink: 0;
    border: 1px solid var(--border2);
    background: var(--bg3);
  }

  .section-title {
    font-size: 20px;
    font-weight: 800;
    color: #fff;
    letter-spacing: -0.5px;
  }

  .section-count {
    font-family: 'Space Mono', monospace;
    font-size: 11px;
    color: var(--text3);
    margin-left: 4px;
  }

  .chevron {
    margin-left: auto;
    color: var(--text3);
    transition: transform 0.3s;
    font-size: 16px;
  }

  .section.collapsed .chevron { transform: rotate(-90deg); }
  .section.collapsed .section-body { display: none; }

  /* ===== SUBCATEGORY ===== */
  .section-body {
    display: flex;
    flex-direction: column;
    gap: 20px;
  }

  .sub-group {
    background: var(--bg2);
    border: 1px solid var(--border);
    border-radius: 12px;
    overflow: hidden;
  }

  .sub-header {
    display: flex;
    align-items: center;
    gap: 10px;
    padding: 14px 18px;
    border-bottom: 1px solid var(--border);
    background: var(--bg3);
  }

  .sub-title {
    font-size: 14px;
    font-weight: 700;
    color: var(--text);
    letter-spacing: 0.2px;
  }

  .sub-badge {
    font-family: 'Space Mono', monospace;
    font-size: 10px;
    padding: 2px 7px;
    border-radius: 3px;
    background: var(--bg4);
    color: var(--text3);
    margin-left: auto;
  }

  .links-grid {
    display: grid;
    grid-template-columns: repeat(auto-fill, minmax(240px, 1fr));
    gap: 1px;
    background: var(--border);
  }

  /* ===== LINK CARDS ===== */
  .link-card {
    display: flex;
    flex-direction: column;
    gap: 6px;
    padding: 14px 18px;
    background: var(--bg2);
    text-decoration: none;
    transition: background 0.15s;
    position: relative;
    overflow: hidden;
  }

  .link-card::before {
    content: '';
    position: absolute;
    left: 0;
    top: 0;
    bottom: 0;
    width: 2px;
    background: var(--accent);
    opacity: 0;
    transition: opacity 0.2s;
  }

  .link-card:hover {
    background: var(--bg3);
  }

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

  .link-name {
    font-size: 14px;
    font-weight: 600;
    color: var(--text);
    display: flex;
    align-items: center;
    gap: 8px;
    transition: color 0.2s;
  }

  .link-card:hover .link-name { color: var(--accent); }

  .link-desc {
    font-family: 'Inter', sans-serif;
    font-size: 12px;
    color: var(--text3);
    line-height: 1.5;
  }

  .link-tags {
    display: flex;
    gap: 4px;
    flex-wrap: wrap;
    margin-top: 2px;
  }

  .link-tag {
    font-family: 'Space Mono', monospace;
    font-size: 10px;
    padding: 2px 6px;
    border-radius: 3px;
    background: var(--bg4);
    color: var(--text3);
  }

  .link-tag.free { color: #4ade80; background: rgba(74,222,128,0.08); }
  .link-tag.interactive { color: var(--accent2); background: rgba(0,191,255,0.08); }
  .link-tag.video { color: #f97316; background: rgba(249,115,22,0.08); }
  .link-tag.practice { color: var(--accent3); background: rgba(124,106,247,0.08); }
  .link-tag.docs { color: #facc15; background: rgba(250,204,21,0.08); }
  .link-tag.cert { color: #ec4899; background: rgba(236,72,153,0.08); }

  .ext-icon {
    font-size: 11px;
    opacity: 0.4;
    transition: opacity 0.2s;
  }

  .link-card:hover .ext-icon { opacity: 0.8; }

  /* ===== NO RESULTS ===== */
  .no-results {
    text-align: center;
    padding: 80px 20px;
    color: var(--text3);
    font-family: 'Space Mono', monospace;
    font-size: 14px;
    display: none;
  }

  /* ===== FOOTER ===== */
  footer {
    position: relative;
    z-index: 1;
    border-top: 1px solid var(--border);
    padding: 28px 40px;
    text-align: center;
    font-family: 'Space Mono', monospace;
    font-size: 11px;
    color: var(--text3);
    letter-spacing: 1px;
  }

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

  /* ===== SCROLLBAR ===== */
  ::-webkit-scrollbar { width: 6px; }
  ::-webkit-scrollbar-track { background: var(--bg); }
  ::-webkit-scrollbar-thumb { background: var(--border2); border-radius: 3px; }
  ::-webkit-scrollbar-thumb:hover { background: var(--text3); }

  /* ===== RESPONSIVE ===== */
  @media (max-width: 768px) {
    header { padding: 0 20px; }
    .nav-tags { display: none; }
    .hero { padding: 48px 20px 32px; }
    .container { padding: 0 20px 60px; }
    .hero h1 { letter-spacing: -1px; }
    footer { padding: 24px 20px; }
  }

  /* ===== PULSE ACCENT GLOW on section icons ===== */
  .section-header:hover .section-icon {
    border-color: var(--accent);
    box-shadow: 0 0 16px var(--glow);
  }

  /* top glow line */
  .section-header::after {
    display: none;
  }

  /* highlight match */
  mark {
    background: rgba(0,229,160,0.25);
    color: var(--accent);
    border-radius: 2px;
    padding: 0 1px;
  }