/* ============ Reset & base ============ */
*, *::before, *::after { box-sizing: border-box; }
html { scroll-behavior: smooth; }
body {
  margin: 0;
  font-family: 'Inter', system-ui, -apple-system, 'PingFang SC', 'Microsoft YaHei', sans-serif;
  background: #0a0e1a;
  color: #e8e8f0;
  font-size: 16px;
  line-height: 1.75;
  -webkit-font-smoothing: antialiased;
}

:root {
  --bg: #0a0e1a;
  --bg-card: #141a2e;
  --bg-elevated: #1d2440;
  --bg-mute: #0f1424;
  --text: #e8e8f0;
  --text-dim: #9ba0b8;
  --text-muted: #6b7090;
  --accent: #ffb86c;
  --accent-2: #8be9fd;
  --highlight: #f1fa8c;
  --pink: #ff79c6;
  --green: #50fa7b;
  --red: #ff5555;
  --border: rgba(255,255,255,0.08);
  --border-strong: rgba(255,255,255,0.16);
}

a { color: var(--accent-2); text-decoration: none; }
a:hover { text-decoration: underline; }

h1, h2, h3 { font-family: 'Noto Serif SC', 'Inter', serif; font-weight: 700; color: var(--text); line-height: 1.3; }

/* ============ Top nav ============ */
.topnav {
  position: sticky;
  top: 0;
  z-index: 100;
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: 14px 32px;
  background: rgba(10, 14, 26, 0.85);
  backdrop-filter: blur(12px);
  border-bottom: 1px solid var(--border);
}
.topnav .logo {
  font-family: 'Noto Serif SC', serif;
  font-weight: 700;
  font-size: 18px;
  color: var(--accent);
}
.topnav ul {
  list-style: none;
  margin: 0; padding: 0;
  display: flex;
  gap: 20px;
}
.topnav a {
  color: var(--text-dim);
  font-size: 14px;
  transition: color 0.15s;
}
.topnav a:hover { color: var(--text); text-decoration: none; }

/* ============ Hero ============ */
.hero {
  padding: 90px 32px 100px;
  background:
    radial-gradient(ellipse at 20% 0%, rgba(255, 184, 108, 0.10) 0%, transparent 50%),
    radial-gradient(ellipse at 80% 100%, rgba(139, 233, 253, 0.08) 0%, transparent 50%),
    var(--bg);
}
.hero-inner {
  max-width: 1000px;
  margin: 0 auto;
}
.hero-eyebrow {
  color: var(--accent);
  font-size: 14px;
  text-transform: uppercase;
  letter-spacing: 2px;
  margin: 0 0 18px;
}
.hero h1 {
  font-size: 48px;
  margin: 0 0 32px;
  letter-spacing: -0.5px;
}
.hero h1 .accent { color: var(--accent); }
.hero-quote {
  margin: 0 0 28px;
  padding: 24px 28px;
  border-left: 3px solid var(--accent);
  background: rgba(255, 184, 108, 0.06);
  font-family: 'Noto Serif SC', serif;
  font-size: 18px;
  line-height: 1.85;
  border-radius: 4px;
}
.hero-quote mark {
  background: rgba(255, 184, 108, 0.18);
  color: var(--highlight);
  padding: 2px 4px;
  border-radius: 3px;
}
.hero-quote p { margin: 0; }
.hero-tag {
  color: var(--text-dim);
  font-size: 16px;
  line-height: 1.9;
  margin-bottom: 36px;
}
.hero-meta {
  display: flex;
  gap: 24px;
  font-size: 13px;
  color: var(--text-muted);
  flex-wrap: wrap;
}
.hero-meta span::before { content: "·  "; color: var(--accent); margin-right: 4px; }

/* ============ Section layout ============ */
.section {
  padding: 80px 32px;
}
.section.alt {
  background: var(--bg-mute);
}
.section-inner {
  max-width: 1000px;
  margin: 0 auto;
}
.step {
  display: inline-block;
  color: var(--accent);
  font-family: 'JetBrains Mono', monospace;
  font-size: 13px;
  letter-spacing: 1.5px;
  text-transform: uppercase;
  margin: 0 0 8px;
  padding: 4px 10px;
  border: 1px solid rgba(255, 184, 108, 0.3);
  border-radius: 3px;
}
.section h2 {
  font-size: 34px;
  margin: 0 0 24px;
  letter-spacing: -0.3px;
}
.section p {
  color: var(--text);
  font-size: 16.5px;
  margin: 0 0 18px;
}
.section strong { color: var(--accent); font-weight: 600; }
.section em { color: var(--accent-2); font-style: normal; }

ul.bullet, ol.steps {
  padding-left: 24px;
  margin: 0 0 24px;
  color: var(--text);
}
ul.bullet li, ol.steps li {
  margin-bottom: 12px;
  line-height: 1.8;
}
ol.steps li::marker { color: var(--accent); font-weight: 600; }

/* ============ Cards ============ */
.cards {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(260px, 1fr));
  gap: 20px;
  margin: 32px 0;
}
.card {
  background: var(--bg-card);
  border: 1px solid var(--border);
  border-radius: 8px;
  padding: 24px;
  transition: transform 0.15s, border-color 0.15s;
}
.card:hover { transform: translateY(-2px); border-color: var(--border-strong); }
.card-tag {
  font-family: 'JetBrains Mono', monospace;
  font-size: 12px;
  color: var(--accent);
  margin: 0 0 12px !important;
  letter-spacing: 1px;
}
.card h3 {
  font-size: 17px;
  margin: 0 0 12px;
  color: var(--text);
}
.card p {
  font-size: 14.5px !important;
  color: var(--text-dim) !important;
  line-height: 1.7;
  margin: 0 !important;
}

/* ============ Callout ============ */
.callout {
  background: linear-gradient(135deg, rgba(139, 233, 253, 0.06), rgba(255, 184, 108, 0.04));
  border: 1px solid rgba(139, 233, 253, 0.18);
  padding: 20px 24px;
  border-radius: 8px;
  margin: 28px 0;
  color: var(--text-dim) !important;
  line-height: 1.85;
}
.callout strong { color: var(--accent-2); }
.callout.final {
  background: linear-gradient(135deg, rgba(255, 184, 108, 0.10), rgba(241, 250, 140, 0.06));
  border-color: rgba(255, 184, 108, 0.3);
}

/* ============ Math callout ============ */
.math-callout {
  background: var(--bg-card);
  border: 1px solid var(--border);
  border-left: 3px solid var(--accent-2);
  padding: 22px 28px;
  border-radius: 6px;
  margin: 28px 0;
  overflow-x: auto;
}
.math-callout .math-cap {
  color: var(--text-dim) !important;
  font-size: 14px !important;
  margin: 12px 0 0 !important;
  font-style: italic;
}

/* ============ Tables ============ */
.dim-table {
  width: 100%;
  border-collapse: collapse;
  margin: 24px 0;
  font-size: 14.5px;
  background: var(--bg-card);
  border-radius: 6px;
  overflow: hidden;
  border: 1px solid var(--border);
}
.dim-table th, .dim-table td {
  padding: 12px 16px;
  text-align: left;
  border-bottom: 1px solid var(--border);
}
.dim-table th {
  background: var(--bg-elevated);
  color: var(--accent);
  font-weight: 600;
  font-size: 13px;
}
.dim-table tr:last-child td { border-bottom: none; }
.dim-table tr:hover { background: rgba(255,255,255,0.02); }

/* ============ Demo cards ============ */
.demo-card {
  background: var(--bg-card);
  border: 1px solid var(--border-strong);
  border-radius: 12px;
  padding: 28px;
  margin: 40px 0;
  box-shadow: 0 8px 24px rgba(0,0,0,0.3);
}
.demo-tag {
  display: inline-block;
  background: rgba(255, 184, 108, 0.12);
  color: var(--accent);
  font-family: 'JetBrains Mono', monospace;
  font-size: 11.5px;
  padding: 4px 10px;
  border-radius: 3px;
  letter-spacing: 1px;
  margin: 0 0 12px !important;
}
.demo-card h3 {
  font-size: 22px;
  margin: 0 0 12px;
  color: var(--text);
}
.demo-desc {
  color: var(--text-dim) !important;
  font-size: 15px !important;
  line-height: 1.75;
  margin-bottom: 24px !important;
}
.demo-stage {
  background: var(--bg-mute);
  border: 1px solid var(--border);
  border-radius: 8px;
  padding: 16px;
  margin-bottom: 16px;
}
.demo-stage canvas {
  display: block;
  width: 100%;
  height: auto;
  max-width: 100%;
  background: #060a14;
  border-radius: 4px;
}
.demo-controls {
  margin-top: 16px;
  display: flex;
  flex-wrap: wrap;
  gap: 16px;
  align-items: center;
  font-size: 14px;
  color: var(--text-dim);
}
.demo-controls label {
  display: flex;
  align-items: center;
  gap: 10px;
  min-width: 200px;
}
.demo-controls label.check { min-width: auto; }
.demo-controls input[type="range"] {
  width: 160px;
  accent-color: var(--accent);
}
.demo-controls input[type="checkbox"] { accent-color: var(--accent); }
.demo-controls button {
  background: var(--bg-elevated);
  border: 1px solid var(--border-strong);
  color: var(--text);
  padding: 7px 16px;
  border-radius: 4px;
  font-family: inherit;
  font-size: 13px;
  cursor: pointer;
  transition: background 0.15s, border-color 0.15s;
}
.demo-controls button:hover { background: rgba(255,255,255,0.06); border-color: var(--accent); }
.demo-controls .stat {
  font-family: 'JetBrains Mono', monospace;
  font-size: 13px;
  color: var(--accent-2);
}
.demo-takeaway {
  margin: 16px 0 0 !important;
  padding: 14px 18px;
  background: rgba(80, 250, 123, 0.05);
  border-left: 2px solid var(--green);
  border-radius: 4px;
  color: var(--text-dim) !important;
  font-size: 14.5px !important;
  line-height: 1.75;
}
.demo-takeaway strong { color: var(--green); }

.cond-buttons {
  display: flex;
  gap: 8px;
  flex-wrap: wrap;
}
.cond-btn {
  background: var(--bg-elevated);
  border: 1px solid var(--border);
  color: var(--text-dim);
  padding: 8px 14px;
  border-radius: 4px;
  cursor: pointer;
  font-size: 13px;
  font-family: inherit;
}
.cond-btn:hover { color: var(--text); border-color: var(--border-strong); }
.cond-btn.active { border-color: var(--accent); color: var(--accent); background: rgba(255,184,108,0.08); }
.cond-btn[data-cond="red"].active   { border-color: var(--red);    color: var(--red);    background: rgba(255,85,85,0.08); }
.cond-btn[data-cond="green"].active { border-color: var(--green);  color: var(--green);  background: rgba(80,250,123,0.08); }
.cond-btn[data-cond="blue"].active  { border-color: var(--accent-2); color: var(--accent-2); background: rgba(139,233,253,0.08); }

/* ============ Reread box ============ */
.reread-box {
  background: var(--bg-card);
  border: 1px solid var(--border);
  border-radius: 8px;
  padding: 28px 32px;
  margin: 32px 0;
}
.reread-line {
  margin: 0 0 22px !important;
  padding-bottom: 22px;
  border-bottom: 1px dashed var(--border);
  line-height: 1.85;
}
.reread-line:last-child { border-bottom: none; padding-bottom: 0; margin-bottom: 0 !important; }
.rr-token {
  font-family: 'Noto Serif SC', serif;
  font-size: 18px;
  color: var(--accent);
  background: rgba(255,184,108,0.10);
  padding: 2px 6px;
  border-radius: 3px;
  display: block;
  margin-bottom: 10px;
}
.rr-token.b { color: var(--text-dim); background: transparent; padding: 0; font-size: 16px; }
.rr-explain {
  color: var(--text-dim);
  font-size: 15px;
  display: block;
  padding-left: 12px;
}
.rr-explain strong { color: var(--accent-2); }

/* ============ Figure caption ============ */
.figure-caption {
  text-align: center;
  background: var(--bg-card);
  border: 1px dashed var(--border-strong);
  padding: 16px;
  border-radius: 6px;
  color: var(--text-dim) !important;
  font-size: 15px !important;
  line-height: 1.85;
  margin: 20px 0 !important;
}

/* ============ Code ============ */
.code-block {
  background: #060a14;
  border: 1px solid var(--border);
  border-radius: 8px;
  padding: 22px 24px;
  margin: 24px 0;
  overflow-x: auto;
  font-family: 'JetBrains Mono', 'SF Mono', monospace;
  font-size: 13.5px;
  line-height: 1.75;
  color: #c8cee0;
}
.code-block code { font-family: inherit; }
.code-block .cmt { color: #6b7090; font-style: italic; }
code {
  background: rgba(255,255,255,0.06);
  padding: 2px 6px;
  border-radius: 3px;
  font-family: 'JetBrains Mono', monospace;
  font-size: 0.92em;
  color: var(--accent-2);
}

ul.refs li { font-size: 15px; color: var(--text-dim); }
ul.refs li strong { color: var(--accent); }

/* ============ Footer ============ */
footer {
  padding: 50px 32px;
  text-align: center;
  background: var(--bg-mute);
  border-top: 1px solid var(--border);
  color: var(--text-muted);
  font-size: 14px;
}
footer .footer-meta { font-size: 12px; margin-top: 12px; opacity: 0.7; }

/* ============ Responsive ============ */
@media (max-width: 760px) {
  .topnav { padding: 12px 16px; flex-direction: column; align-items: flex-start; gap: 8px; }
  .topnav ul { flex-wrap: wrap; gap: 14px; }
  .hero { padding: 60px 20px 70px; }
  .hero h1 { font-size: 32px; }
  .hero-quote { font-size: 16px; padding: 18px 20px; }
  .section { padding: 56px 20px; }
  .section h2 { font-size: 26px; }
  .demo-card { padding: 20px; }
  .demo-controls label { min-width: 100%; }
  .demo-controls input[type="range"] { flex: 1; width: auto; }
  .dim-table { font-size: 13px; }
  .dim-table th, .dim-table td { padding: 8px 10px; }
}