:root {
      --bg:        #06090f;
      --bg2:       #0d1220;
      --bg3:       #111827;
      --accent:    #38bdf8;
      --accent2:   #818cf8;
      --accent3:   #34d399;
      --amber:     #fbbf24;
      --pink:      #f472b6;
      --text:      #e2e8f0;
      --muted:     #8899aa;
      --border:    #1e2d40;
      --glow:      0 0 18px rgba(56,189,248,0.25);
      --glow2:     0 0 18px rgba(129,140,248,0.25);
      --radius:    14px;
    }

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

    html { scroll-behavior: smooth; }

    body {
      background: var(--bg);
      color: var(--text);
      font-family: 'Segoe UI', system-ui, -apple-system, sans-serif;
      font-size: 16px;
      line-height: 1.75;
    }

    /* ── scrollbar ── */
    ::-webkit-scrollbar { width: 7px; }
    ::-webkit-scrollbar-track { background: var(--bg); }
    ::-webkit-scrollbar-thumb { background: #1e3a5f; border-radius: 4px; }

    /* ── HERO ── */
    .hero {
      position: relative;
      overflow: hidden;
      padding: 100px 20px 80px;
      text-align: center;
      background: radial-gradient(ellipse 80% 60% at 50% 0%, #0a1f3a 0%, var(--bg) 70%);
      border-bottom: 1px solid var(--border);
    }

    .hero::before {
      content: '';
      position: absolute;
      inset: 0;
      background:
        radial-gradient(circle at 20% 50%, rgba(56,189,248,0.07) 0%, transparent 50%),
        radial-gradient(circle at 80% 30%, rgba(129,140,248,0.07) 0%, transparent 50%);
      pointer-events: none;
    }

    /* particle dots */
    .hero-dots {
      position: absolute;
      inset: 0;
      pointer-events: none;
    }
    .hero-dots span {
      position: absolute;
      border-radius: 50%;
      background: var(--accent);
      opacity: 0;
      animation: blink 4s infinite;
    }
    @keyframes blink {
      0%,100% { opacity: 0; transform: scale(1); }
      50%      { opacity: 0.6; transform: scale(1.4); }
    }

    .badge {
      display: inline-block;
      background: rgba(56,189,248,0.12);
      border: 1px solid rgba(56,189,248,0.35);
      color: var(--accent);
      font-size: 0.72rem;
      letter-spacing: 0.14em;
      text-transform: uppercase;
      padding: 4px 14px;
      border-radius: 100px;
      margin-bottom: 22px;
    }

    .hero h1 {
      font-size: clamp(2rem, 5vw, 3.6rem);
      font-weight: 800;
      letter-spacing: -0.02em;
      line-height: 1.15;
      background: linear-gradient(135deg, #e0f2fe 0%, var(--accent) 40%, var(--accent2) 100%);
      -webkit-background-clip: text;
      -webkit-text-fill-color: transparent;
      background-clip: text;
      margin-bottom: 18px;
    }

    .hero-sub {
      max-width: 720px;
      margin: 0 auto 36px;
      color: var(--muted);
      font-size: 1.05rem;
    }

    .hero-tags {
      display: flex;
      justify-content: center;
      flex-wrap: wrap;
      gap: 10px;
    }
    .tag {
      background: rgba(255,255,255,0.04);
      border: 1px solid var(--border);
      color: var(--muted);
      font-size: 0.8rem;
      padding: 5px 14px;
      border-radius: 100px;
    }

    /* ── NAV ── */
    .sticky-nav {
      position: sticky;
      top: 0;
      z-index: 100;
      background: rgba(6,9,15,0.88);
      backdrop-filter: blur(14px);
      border-bottom: 1px solid var(--border);
      padding: 0 24px;
      display: flex;
      justify-content: center;
      gap: 0;
      overflow-x: auto;
    }
    .sticky-nav a {
      display: inline-block;
      padding: 14px 18px;
      font-size: 0.82rem;
      color: var(--muted);
      text-decoration: none;
      white-space: nowrap;
      border-bottom: 2px solid transparent;
      transition: color .2s, border-color .2s;
    }
    .sticky-nav a:hover {
      color: var(--accent);
      border-bottom-color: var(--accent);
    }

    /* ── LAYOUT ── */
    .page { max-width: 1060px; margin: 0 auto; padding: 60px 24px; }

    /* ── SECTION HEADERS ── */
    .sec-header {
      display: flex;
      align-items: center;
      gap: 14px;
      margin-bottom: 36px;
    }
    .sec-icon {
      width: 46px; height: 46px;
      border-radius: 12px;
      display: flex; align-items: center; justify-content: center;
      font-size: 1.3rem;
      flex-shrink: 0;
    }
    .ic-blue  { background: rgba(56,189,248,0.12);  border: 1px solid rgba(56,189,248,0.3); }
    .ic-indigo{ background: rgba(129,140,248,0.12); border: 1px solid rgba(129,140,248,0.3); }
    .ic-green { background: rgba(52,211,153,0.12);  border: 1px solid rgba(52,211,153,0.3); }
    .ic-amber { background: rgba(251,191,36,0.12);  border: 1px solid rgba(251,191,36,0.3); }
    .ic-pink  { background: rgba(244,114,182,0.12); border: 1px solid rgba(244,114,182,0.3); }

    .sec-title h2 {
      font-size: 1.55rem;
      font-weight: 700;
      color: var(--text);
    }
    .sec-title span {
      font-size: 0.78rem;
      color: var(--muted);
      letter-spacing: 0.08em;
      text-transform: uppercase;
    }

    /* ── SEPARATOR ── */
    .sep {
      height: 1px;
      background: linear-gradient(90deg, transparent, var(--border), transparent);
      margin: 60px 0;
    }

    /* ── CARDS ── */
    .card {
      background: var(--bg2);
      border: 1px solid var(--border);
      border-radius: var(--radius);
      padding: 24px 28px;
      transition: border-color .25s, box-shadow .25s;
    }
    .card:hover {
      border-color: rgba(56,189,248,0.3);
      box-shadow: var(--glow);
    }

    .grid-2 { display: grid; grid-template-columns: 1fr 1fr; gap: 20px; }
    .grid-3 { display: grid; grid-template-columns: repeat(3,1fr); gap: 20px; }
    .grid-4 { display: grid; grid-template-columns: repeat(4,1fr); gap: 18px; }

    @media(max-width:900px) {
      .grid-3,.grid-4 { grid-template-columns: 1fr 1fr; }
    }
    @media(max-width:600px) {
      .grid-2,.grid-3,.grid-4 { grid-template-columns: 1fr; }
    }

    .card-title {
      font-size: 0.95rem;
      font-weight: 600;
      margin-bottom: 8px;
      display: flex;
      align-items: center;
      gap: 8px;
    }
    .dot-blue   { width:8px;height:8px;border-radius:50%;background:var(--accent); flex-shrink:0; }
    .dot-indigo { width:8px;height:8px;border-radius:50%;background:var(--accent2); flex-shrink:0; }
    .dot-green  { width:8px;height:8px;border-radius:50%;background:var(--accent3); flex-shrink:0; }
    .dot-amber  { width:8px;height:8px;border-radius:50%;background:var(--amber); flex-shrink:0; }
    .dot-pink   { width:8px;height:8px;border-radius:50%;background:var(--pink);  flex-shrink:0; }

    .card p, .card li { font-size: 0.9rem; color: #94a3b8; }
    .card ul { padding-left: 18px; }
    .card li { margin-bottom: 4px; }

    /* highlight blocks */
    .callout {
      border-radius: var(--radius);
      padding: 20px 24px;
      margin: 24px 0;
      font-size: 0.9rem;
    }
    .callout-blue  { background: rgba(56,189,248,0.07);  border-left: 3px solid var(--accent); }
    .callout-indigo{ background: rgba(129,140,248,0.07); border-left: 3px solid var(--accent2); }
    .callout-green { background: rgba(52,211,153,0.07);  border-left: 3px solid var(--accent3); }
    .callout-amber { background: rgba(251,191,36,0.07);  border-left: 3px solid var(--amber); }
    .callout-pink  { background: rgba(244,114,182,0.07); border-left: 3px solid var(--pink); }

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

    /* ── MAIXIE CARDS ── */
    .maixie-card {
      background: linear-gradient(135deg, rgba(129,140,248,0.07) 0%, rgba(244,114,182,0.07) 100%);
      border: 1px solid rgba(129,140,248,0.25);
      border-radius: var(--radius);
      padding: 22px 26px;
    }
    .maixie-card .maixie-label {
      font-size: 0.7rem;
      letter-spacing: 0.12em;
      text-transform: uppercase;
      color: var(--pink);
      margin-bottom: 10px;
      font-weight: 600;
    }
    .maixie-card p, .maixie-card li { font-size: 0.88rem; color: #c4b5fd; }
    .maixie-card ul { padding-left: 18px; }
    .maixie-card li { margin-bottom: 5px; }

    /* ── TOPOLOGY GRID ── */
    .topo-card {
      background: var(--bg2);
      border: 1px solid var(--border);
      border-radius: var(--radius);
      padding: 22px 20px;
      text-align: center;
    }
    .topo-icon { font-size: 2.2rem; margin-bottom: 12px; }
    .topo-name { font-size: 0.95rem; font-weight: 600; color: var(--text); margin-bottom: 8px; }
    .topo-desc { font-size: 0.82rem; color: var(--muted); }

    /* ── ANALOGY TABLE ── */
    .analogy-table {
      width: 100%;
      border-collapse: collapse;
      font-size: 0.88rem;
    }
    .analogy-table th {
      background: rgba(56,189,248,0.1);
      color: var(--accent);
      padding: 12px 16px;
      text-align: left;
      font-weight: 600;
      font-size: 0.8rem;
      letter-spacing: 0.06em;
      text-transform: uppercase;
      border-bottom: 1px solid var(--border);
    }
    .analogy-table td {
      padding: 11px 16px;
      border-bottom: 1px solid var(--border);
      color: #94a3b8;
      vertical-align: top;
    }
    .analogy-table tr:last-child td { border-bottom: none; }
    .analogy-table tr:hover td { background: rgba(255,255,255,0.02); }
    .analogy-table td:first-child { color: var(--text); font-weight: 500; }
    .analogy-table td:nth-child(2) { color: #7dd3fc; }
    .analogy-table td:nth-child(3) { color: #a5b4fc; }

    /* ── STEP TIMELINE ── */
    .timeline { display: flex; flex-direction: column; gap: 0; }
    .timeline-item {
      display: grid;
      grid-template-columns: 60px 1fr;
      gap: 20px;
      position: relative;
    }
    .timeline-item:not(:last-child)::before {
      content: '';
      position: absolute;
      left: 29px;
      top: 50px;
      bottom: -20px;
      width: 2px;
      background: linear-gradient(180deg, var(--accent) 0%, transparent 100%);
      opacity: 0.25;
    }
    .timeline-num {
      width: 44px; height: 44px;
      border-radius: 50%;
      background: rgba(56,189,248,0.12);
      border: 2px solid rgba(56,189,248,0.4);
      display: flex; align-items: center; justify-content: center;
      font-weight: 700;
      font-size: 0.95rem;
      color: var(--accent);
      flex-shrink: 0;
      margin-top: 4px;
    }
    .timeline-body {
      background: var(--bg2);
      border: 1px solid var(--border);
      border-radius: var(--radius);
      padding: 20px 24px;
      margin-bottom: 20px;
    }
    .timeline-body h3 { font-size: 1rem; color: var(--text); margin-bottom: 10px; }
    .timeline-body p, .timeline-body li { font-size: 0.88rem; color: #94a3b8; }
    .timeline-body ul { padding-left: 18px; }
    .timeline-body li { margin-bottom: 4px; }

    /* ── PROTOCOL STACK ── */
    .stack {
      display: flex;
      flex-direction: column;
      gap: 6px;
    }
    .stack-layer {
      border-radius: 10px;
      padding: 16px 22px;
      display: flex;
      align-items: center;
      gap: 16px;
    }
    .sl-num {
      font-size: 0.75rem;
      font-weight: 700;
      color: var(--muted);
      width: 24px;
      text-align: center;
    }
    .sl-name { font-size: 0.95rem; font-weight: 600; flex: 0 0 160px; }
    .sl-desc { font-size: 0.85rem; color: var(--muted); }

    .sl-app   { background: rgba(244,114,182,0.1); border: 1px solid rgba(244,114,182,0.25); }
    .sl-app   .sl-name { color: var(--pink); }
    .sl-trans { background: rgba(251,191,36,0.1);  border: 1px solid rgba(251,191,36,0.25); }
    .sl-trans .sl-name { color: var(--amber); }
    .sl-net   { background: rgba(52,211,153,0.1);  border: 1px solid rgba(52,211,153,0.25); }
    .sl-net   .sl-name { color: var(--accent3); }
    .sl-link  { background: rgba(56,189,248,0.1);  border: 1px solid rgba(56,189,248,0.25); }
    .sl-link  .sl-name { color: var(--accent); }
    .sl-phys  { background: rgba(129,140,248,0.1); border: 1px solid rgba(129,140,248,0.25); }
    .sl-phys  .sl-name { color: var(--accent2); }

    /* ── FRAME FORMAT ── */
    .frame-vis {
      display: flex;
      border-radius: 10px;
      overflow: hidden;
      font-size: 0.78rem;
      font-weight: 600;
      text-align: center;
      margin: 16px 0;
    }
    .fv-pream { background: rgba(56,189,248,0.2);  color: var(--accent);  padding: 14px 10px; flex: 1.2; }
    .fv-head  { background: rgba(251,191,36,0.2);  color: var(--amber);   padding: 14px 10px; flex: 1.5; }
    .fv-pay   { background: rgba(52,211,153,0.2);  color: var(--accent3); padding: 14px 10px; flex: 3; }
    .fv-crc   { background: rgba(244,114,182,0.2); color: var(--pink);    padding: 14px 10px; flex: 0.8; }
    .frame-vis div small { display:block; font-weight:400; color: rgba(255,255,255,0.5); font-size:0.7rem; margin-top:4px; }

    /* ── STAT CARDS ── */
    .stat-card {
      background: var(--bg2);
      border: 1px solid var(--border);
      border-radius: var(--radius);
      padding: 22px 20px;
      text-align: center;
    }
    .stat-num {
      font-size: 1.75rem;
      font-weight: 800;
      line-height: 1;
      margin-bottom: 6px;
    }
    .stat-label { font-size: 0.8rem; color: var(--muted); }
    .c-blue   { color: var(--accent); }
    .c-indigo { color: var(--accent2); }
    .c-green  { color: var(--accent3); }
    .c-amber  { color: var(--amber); }
    .c-pink   { color: var(--pink); }

    /* ── FOOTER ── */
    footer {
      border-top: 1px solid var(--border);
      padding: 36px 24px;
      text-align: center;
      color: var(--muted);
      font-size: 0.82rem;
    }
    footer strong { color: var(--text); }

    /* ── helpers ── */
    .mt-16 { margin-top: 16px; }
    .mt-24 { margin-top: 24px; }
    .mt-32 { margin-top: 32px; }
    .mb-16 { margin-bottom: 16px; }
    h3.sub { font-size: 1rem; color: var(--text); font-weight: 600; margin: 22px 0 10px; }
    p.body { font-size: 0.92rem; color: #94a3b8; margin-bottom: 14px; }
    code { background: rgba(56,189,248,0.1); color: var(--accent); font-size: 0.82em; padding: 2px 7px; border-radius: 5px; font-family: 'Cascadia Code','Fira Code',monospace; }

    /* ── INTRO PHYSICS ── */
    .phys-grid { display: grid; grid-template-columns: 1fr 1fr; gap: 20px; margin-top: 20px; }
    @media(max-width:640px) { .phys-grid { grid-template-columns: 1fr; } }

    /* ── NEUTRINO TYPE TABLE ── */
    .type-table { width:100%; border-collapse:collapse; font-size:0.86rem; margin-top:16px; }
    .type-table th { background: rgba(52,211,153,0.1); color: var(--accent3); padding:10px 14px; text-align:left; border-bottom:1px solid var(--border); }
    .type-table td { padding:9px 14px; border-bottom:1px solid var(--border); color:#94a3b8; }
    .type-table td:first-child { color: var(--text); font-weight:500; }
    .type-table tr:last-child td { border-bottom:none; }