:root {
  --bg: #0b0d17;
  --bg-alt: #10132194;
  --card: #151832;
  --card-border: #262b4d;
  --text: #e8e9f5;
  --text-dim: #a8adc9;
  --accent: #7c9bff;
  --accent2: #ff8ab8;
  --accent3: #6ee7c8;
  --radius: 16px;
}

* { box-sizing: border-box; }

html { scroll-behavior: smooth; }

body {
  margin: 0;
  background: var(--bg);
  color: var(--text);
  font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Helvetica, Arial, sans-serif;
  line-height: 1.6;
}

.progress-bar {
  position: fixed;
  top: 0; left: 0;
  height: 3px;
  width: 0%;
  background: linear-gradient(90deg, var(--accent), var(--accent2));
  z-index: 1000;
  transition: width 0.1s ease-out;
}

.topnav {
  position: sticky;
  top: 0;
  z-index: 100;
  display: flex;
  justify-content: space-between;
  align-items: center;
  padding: 14px 32px;
  background: rgba(11, 13, 23, 0.85);
  backdrop-filter: blur(10px);
  border-bottom: 1px solid var(--card-border);
  flex-wrap: wrap;
  gap: 10px;
}

.topnav .brand { font-weight: 700; }

.topnav .links { display: flex; gap: 18px; flex-wrap: wrap; }

.topnav a {
  color: var(--text-dim);
  text-decoration: none;
  font-size: 0.92rem;
  transition: color 0.2s;
}
.topnav a:hover { color: var(--accent); }

.hero {
  position: relative;
  height: 92vh;
  min-height: 500px;
  display: flex;
  align-items: center;
  justify-content: center;
  overflow: hidden;
  border-bottom: 1px solid var(--card-border);
}

#heroCanvas {
  position: absolute;
  inset: 0;
  width: 100%;
  height: 100%;
}

.hero-content {
  position: relative;
  z-index: 2;
  text-align: center;
  padding: 0 20px;
}

.hero h1 {
  font-size: clamp(2.5rem, 7vw, 5rem);
  margin: 0;
  background: linear-gradient(90deg, var(--accent), var(--accent2), var(--accent3));
  -webkit-background-clip: text;
  background-clip: text;
  color: transparent;
  letter-spacing: -0.02em;
}

.scroll-cue {
  display: inline-block;
  margin-top: 40px;
  color: var(--text-dim);
  text-decoration: none;
  animation: bob 2s infinite ease-in-out;
}

@keyframes bob {
  0%, 100% { transform: translateY(0); }
  50% { transform: translateY(8px); }
}

main { max-width: 980px; margin: 0 auto; padding: 0 24px; }

.section {
  padding: 90px 0;
  border-bottom: 1px solid var(--card-border);
}
.section:last-of-type { border-bottom: none; }

.section h2 {
  font-size: clamp(1.6rem, 3.4vw, 2.3rem);
  margin-bottom: 20px;
}

.lead {
  color: var(--text-dim);
  font-size: 1.08rem;
  max-width: 760px;
}

blockquote {
  border-left: 3px solid var(--accent);
  margin: 24px 0;
  padding: 10px 20px;
  color: var(--text);
  font-style: italic;
  background: var(--bg-alt);
  border-radius: 0 var(--radius) var(--radius) 0;
}

.reveal {
  opacity: 0;
  transform: translateY(24px);
  transition: opacity 0.7s ease, transform 0.7s ease;
}
.reveal.visible {
  opacity: 1;
  transform: translateY(0);
}

.analogy-grid {
  display: grid;
  grid-template-columns: 1fr auto 1fr;
  gap: 16px;
  align-items: center;
  margin: 36px 0;
}

.analogy-card {
  background: var(--card);
  border: 1px solid var(--card-border);
  border-radius: var(--radius);
  padding: 24px;
  text-align: center;
}
.arrow-card { background: transparent; border: none; }
.analogy-card .emoji { font-size: 2.6rem; margin-bottom: 8px; }
.analogy-card h3 { margin: 6px 0; font-size: 1.05rem; }
.analogy-card p { color: var(--text-dim); font-size: 0.92rem; margin: 0; }

@media (max-width: 640px) {
  .analogy-grid { grid-template-columns: 1fr; }
  .arrow-card { transform: rotate(90deg); }
}

.demo-box {
  background: var(--card);
  border: 1px solid var(--card-border);
  border-radius: var(--radius);
  padding: 20px;
  margin-top: 28px;
}

.demo-box canvas {
  width: 100%;
  height: auto;
  display: block;
  background: #0a0c18;
  border-radius: 12px;
  border: 1px solid var(--card-border);
}

.demo-controls {
  display: flex;
  align-items: center;
  gap: 16px;
  flex-wrap: wrap;
  margin-top: 16px;
}

.demo-controls button {
  background: linear-gradient(135deg, var(--accent), #5a6fe0);
  color: white;
  border: none;
  padding: 10px 18px;
  border-radius: 999px;
  font-weight: 600;
  cursor: pointer;
  font-size: 0.9rem;
  transition: transform 0.15s ease, opacity 0.15s ease;
}
.demo-controls button:hover { transform: translateY(-1px); opacity: 0.92; }
.demo-controls button:active { transform: translateY(0); }

.slider-label {
  display: flex;
  align-items: center;
  gap: 10px;
  color: var(--text-dim);
  font-size: 0.9rem;
  font-variant-numeric: tabular-nums;
}

.slider-label input[type="range"] {
  width: 220px;
  accent-color: var(--accent);
}

.toggle-label {
  display: flex;
  align-items: center;
  gap: 8px;
  color: var(--text-dim);
  font-size: 0.9rem;
}

.caption {
  color: var(--text-dim);
  font-size: 0.92rem;
  margin-top: 14px;
  margin-bottom: 0;
}

.steps {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(170px, 1fr));
  gap: 16px;
  margin: 32px 0;
}

.step {
  background: var(--card);
  border: 1px solid var(--card-border);
  border-radius: var(--radius);
  padding: 20px;
  position: relative;
}

.step-num {
  position: absolute;
  top: -10px;
  right: -10px;
  width: 28px;
  height: 28px;
  border-radius: 50%;
  background: linear-gradient(135deg, var(--accent2), var(--accent));
  display: flex;
  align-items: center;
  justify-content: center;
  font-weight: 700;
  font-size: 0.85rem;
}

.step h3 { margin: 0 0 8px; font-size: 1rem; }
.step p { color: var(--text-dim); font-size: 0.88rem; margin: 0; }

.callout {
  background: linear-gradient(135deg, #1c2044, #241a3a);
  border: 1px solid var(--card-border);
  border-radius: var(--radius);
  padding: 20px 24px;
  color: var(--text);
  font-size: 0.98rem;
}

.phase-grid {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 20px;
  margin: 30px 0;
  align-items: start;
}

@media (max-width: 780px) {
  .phase-grid { grid-template-columns: 1fr; }
}

.phase-card {
  background: var(--card);
  border: 1px solid var(--card-border);
  border-radius: var(--radius);
  padding: 22px;
  position: relative;
}

.phase-badge {
  display: inline-block;
  background: linear-gradient(135deg, var(--accent), var(--accent2));
  color: #0b0d17;
  font-weight: 700;
  font-size: 0.72rem;
  letter-spacing: 0.04em;
  text-transform: uppercase;
  padding: 4px 10px;
  border-radius: 999px;
  margin-bottom: 12px;
}

.phase-card h3 {
  font-size: 1.1rem;
  margin: 0 0 16px;
  line-height: 1.4;
}

.phase-when {
  display: block;
  font-weight: 400;
  font-size: 0.82rem;
  color: var(--text-dim);
  margin-top: 2px;
}

.loop-diagram {
  display: flex;
  flex-direction: column;
  gap: 8px;
}

.loop-step {
  display: flex;
  align-items: center;
  gap: 10px;
  background: var(--bg-alt);
  border: 1px solid var(--card-border);
  border-radius: 10px;
  padding: 10px 12px;
  font-size: 0.86rem;
  color: var(--text-dim);
  transition: background 0.3s ease, border-color 0.3s ease, color 0.3s ease, transform 0.3s ease;
}

.loop-step.active {
  background: rgba(124, 155, 255, 0.14);
  border-color: var(--accent);
  color: var(--text);
  transform: translateX(3px);
}

.loop-num {
  flex-shrink: 0;
  width: 20px;
  height: 20px;
  border-radius: 50%;
  background: var(--card-border);
  display: flex;
  align-items: center;
  justify-content: center;
  font-size: 0.72rem;
  font-weight: 700;
  color: var(--text-dim);
  transition: background 0.3s ease, color 0.3s ease;
}

.loop-step.active .loop-num {
  background: var(--accent);
  color: #0b0d17;
}

.loop-repeat {
  margin-top: 14px;
  text-align: center;
  font-size: 0.82rem;
  color: var(--accent3);
  border: 1px dashed var(--card-border);
  border-radius: 10px;
  padding: 8px;
}

.gen-diagram {
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  justify-content: center;
  gap: 8px;
  padding: 10px 0 4px;
}

.gen-step {
  background: var(--bg-alt);
  border: 1px solid var(--card-border);
  border-radius: 10px;
  padding: 10px 12px;
  font-size: 0.78rem;
  color: var(--text-dim);
  text-align: center;
  min-width: 78px;
  transition: background 0.3s ease, border-color 0.3s ease, color 0.3s ease;
}

.gen-step.active {
  background: rgba(255, 138, 184, 0.16);
  border-color: var(--accent2);
  color: var(--text);
}

.gen-arrow {
  color: var(--text-dim);
  font-size: 1.1rem;
}

.phase-note {
  color: var(--text-dim);
  font-size: 0.86rem;
  margin: 14px 0 0;
}

.why-card {
  background: var(--card);
  border: 1px solid var(--card-border);
  border-radius: var(--radius);
  padding: 20px 24px;
  margin-bottom: 16px;
}

.why-card h3 {
  margin: 0 0 8px;
  font-size: 1.05rem;
  color: var(--accent);
}

.why-card p {
  margin: 0;
  color: var(--text-dim);
  font-size: 0.94rem;
}

.compare-grid {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 20px;
  margin: 30px 0;
}

.compare-box {
  background: var(--card);
  border: 1px solid var(--card-border);
  border-radius: var(--radius);
  padding: 18px;
  text-align: center;
}
.compare-box h3 { margin-top: 0; }
.compare-box canvas {
  width: 100%;
  height: auto;
  background: #0a0c18;
  border-radius: 10px;
  border: 1px solid var(--card-border);
}
.compare-box p { color: var(--text-dim); font-size: 0.88rem; margin-bottom: 0; }

@media (max-width: 640px) {
  .compare-grid { grid-template-columns: 1fr; }
}

.compare-table {
  width: 100%;
  border-collapse: collapse;
  margin-top: 30px;
  font-size: 0.92rem;
}
.compare-table th, .compare-table td {
  border: 1px solid var(--card-border);
  padding: 12px 14px;
  text-align: left;
}
.compare-table th {
  background: var(--card);
  color: var(--accent);
}
.compare-table td:first-child { color: var(--text-dim); font-weight: 600; }

.math-details {
  background: var(--card);
  border: 1px solid var(--card-border);
  border-radius: var(--radius);
  padding: 18px 22px;
}
.math-details summary {
  cursor: pointer;
  font-weight: 600;
  color: var(--accent);
  outline: none;
}
.math-content { margin-top: 18px; }

.formula-card {
  background: var(--bg-alt);
  border: 1px solid var(--card-border);
  border-radius: 12px;
  padding: 16px 20px;
  margin: 14px 0;
}
.formula {
  font-family: "SF Mono", Menlo, Consolas, monospace;
  font-size: 1.15rem;
  color: var(--accent3);
  margin-bottom: 6px;
}
.formula-card p { margin: 0; color: var(--text-dim); font-size: 0.9rem; }

.derivation-step {
  margin: 28px 0;
  padding-top: 20px;
  border-top: 1px solid var(--card-border);
}
.derivation-step:first-of-type {
  margin-top: 22px;
  padding-top: 0;
  border-top: none;
}

.derivation-tag {
  display: inline-block;
  font-size: 0.72rem;
  font-weight: 700;
  letter-spacing: 0.05em;
  text-transform: uppercase;
  color: var(--accent3);
  border: 1px solid var(--card-border);
  border-radius: 999px;
  padding: 3px 10px;
  margin-bottom: 8px;
}

.derivation-step h4 {
  margin: 4px 0 10px;
  font-size: 1rem;
  color: var(--text);
}

.derivation-step p {
  color: var(--text-dim);
  font-size: 0.92rem;
}

.derivation-box {
  background: #05060d;
  border: 1px solid var(--card-border);
  border-radius: 10px;
  padding: 14px 18px;
  margin: 12px 0;
  overflow-x: auto;
}

.deriv-line {
  font-family: "SF Mono", Menlo, Consolas, monospace;
  font-size: 0.95rem;
  color: var(--text-dim);
  white-space: pre;
  line-height: 1.7;
}

.deriv-line.deriv-final {
  color: var(--accent3);
  font-weight: 600;
}

.deriv-note {
  color: var(--text-dim);
  font-size: 0.88rem;
  font-style: italic;
}

.uses-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(190px, 1fr));
  gap: 16px;
  margin-top: 30px;
}
.use-card {
  background: var(--card);
  border: 1px solid var(--card-border);
  border-radius: var(--radius);
  padding: 22px;
  text-align: center;
}
.use-card .emoji { font-size: 2.2rem; }
.use-card h3 { margin: 10px 0 6px; font-size: 1rem; }
.use-card p { color: var(--text-dim); font-size: 0.85rem; margin: 0; }

.flip-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(180px, 1fr));
  gap: 16px;
  margin-top: 30px;
}

.flip-card {
  perspective: 1000px;
  height: 130px;
  cursor: pointer;
}
.flip-inner {
  position: relative;
  width: 100%;
  height: 100%;
  transition: transform 0.6s;
  transform-style: preserve-3d;
}
.flip-card.flipped .flip-inner { transform: rotateY(180deg); }

.flip-front, .flip-back {
  position: absolute;
  inset: 0;
  backface-visibility: hidden;
  border-radius: var(--radius);
  display: flex;
  align-items: center;
  justify-content: center;
  text-align: center;
  padding: 16px;
  font-size: 0.92rem;
}
.flip-front {
  background: linear-gradient(135deg, var(--card), #1a1e3d);
  border: 1px solid var(--card-border);
  font-weight: 700;
  font-size: 1.1rem;
  color: var(--accent);
}
.flip-back {
  background: linear-gradient(135deg, #1c2044, #241a3a);
  border: 1px solid var(--card-border);
  color: var(--text-dim);
  transform: rotateY(180deg);
}

footer {
  text-align: center;
  padding: 40px 20px;
  color: var(--text-dim);
  font-size: 0.85rem;
}

code {
  background: var(--bg-alt);
  padding: 2px 6px;
  border-radius: 6px;
  font-size: 0.9em;
}

/* ================= DPO page additions ================= */

:root {
  --good: #6ee7c8;
  --bad: #ff8ab8;
}

a { color: var(--accent); }

.topnav .brand { display: flex; align-items: center; gap: 14px; }
.topnav .brand .home-link { font-weight: 400; font-size: 0.85rem; }

.hero-sub {
  margin: 6px 0 0;
  font-size: clamp(1.1rem, 2.6vw, 1.6rem);
  font-weight: 600;
  color: var(--text);
  letter-spacing: 0.01em;
}

.good { color: var(--good); }
.bad { color: var(--bad); }

.good-card { border-color: rgba(110, 231, 200, 0.45); }
.bad-card { border-color: rgba(255, 138, 184, 0.45); }

.katex { font-size: 1.08em; }
.katex-display {
  overflow-x: auto;
  overflow-y: hidden;
  padding: 4px 0;
  margin: 0.6em 0;
}

.sub-h {
  margin: 44px 0 6px;
  font-size: 1.25rem;
}

.fine {
  display: block;
  margin-top: 8px;
  font-size: 0.8rem;
  opacity: 0.75;
}

/* ---------- pair demo ---------- */
.prompt-card {
  background: var(--bg-alt);
  border: 1px solid var(--card-border);
  border-radius: 12px;
  padding: 12px 16px;
  margin-bottom: 16px;
}
.prompt-card p { margin: 6px 0 0; font-size: 1rem; }
.tag {
  display: inline-block;
  font-size: 0.72rem;
  font-weight: 700;
  letter-spacing: 0.05em;
  text-transform: uppercase;
  color: var(--accent);
}

.resp-grid {
  display: grid;
  grid-template-columns: 1fr auto 1fr;
  gap: 14px;
  align-items: stretch;
}
@media (max-width: 700px) {
  .resp-grid { grid-template-columns: 1fr; }
}

.resp-card {
  background: var(--bg-alt);
  border: 2px solid var(--card-border);
  border-radius: 14px;
  padding: 14px 16px;
  transition: border-color 0.5s ease, box-shadow 0.5s ease, transform 0.5s ease, opacity 0.5s ease;
  min-height: 150px;
}
.resp-card.chosen {
  border-color: var(--good);
  box-shadow: 0 0 26px rgba(110, 231, 200, 0.25);
  transform: translateY(-3px);
}
.resp-card.rejected {
  border-color: var(--bad);
  box-shadow: 0 0 18px rgba(255, 138, 184, 0.15);
  opacity: 0.8;
}
.resp-badge {
  display: inline-block;
  font-size: 0.75rem;
  font-weight: 700;
  padding: 3px 10px;
  border-radius: 999px;
  background: var(--card-border);
  color: var(--text-dim);
  margin-bottom: 10px;
  transition: background 0.4s ease, color 0.4s ease;
}
.resp-card.chosen .resp-badge { background: var(--good); color: #0b0d17; }
.resp-card.rejected .resp-badge { background: var(--bad); color: #0b0d17; }
.resp-body { color: var(--text-dim); font-size: 0.93rem; }
.resp-body canvas {
  width: 100%;
  height: auto;
  display: block;
  border-radius: 10px;
}

.judge {
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: center;
  gap: 6px;
  min-width: 110px;
  text-align: center;
}
.judge-emoji { font-size: 2.4rem; transition: transform 0.3s ease; }
.judge-text { font-size: 0.8rem; color: var(--text-dim); max-width: 120px; }
.judge.thinking .judge-emoji { animation: think 0.6s ease-in-out infinite alternate; }
@keyframes think {
  from { transform: rotate(-12deg) scale(1); }
  to { transform: rotate(12deg) scale(1.1); }
}

/* ---------- shared bits ---------- */
.badge-pink { background: linear-gradient(135deg, var(--accent2), #b07cff); }
.callout { margin-top: 28px; }
.plan-intro { margin: 0 0 14px; }
.plan-list {
  list-style: none;
  margin: 0;
  padding: 0;
  display: grid;
  grid-template-columns: repeat(4, 1fr);
  gap: 10px;
}
@media (max-width: 860px) {
  .plan-list { grid-template-columns: repeat(2, 1fr); }
}
@media (max-width: 420px) {
  .plan-list { grid-template-columns: 1fr; }
}
.plan-list a {
  display: flex;
  align-items: center;
  gap: 10px;
  height: 100%;
  box-sizing: border-box;
  padding: 10px 12px;
  background: rgba(11, 13, 23, 0.45);
  border: 1px solid var(--card-border);
  border-radius: 12px;
  color: var(--text);
  text-decoration: none;
  font-size: 0.92rem;
  line-height: 1.35;
  transition: border-color 0.2s ease, transform 0.2s ease;
}
.plan-list a:hover { border-color: var(--accent); transform: translateY(-2px); }
.plan-list .sec-num { flex: none; margin-right: 0; vertical-align: 0; }
.build-formula { color: var(--text); }
.build-formula .katex-display { margin: 0.4em 0; }

.sec-num {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  width: 1.6em;
  height: 1.6em;
  margin-right: 10px;
  border-radius: 50%;
  background: linear-gradient(135deg, var(--accent2), var(--accent));
  color: #0b0d17;
  font-size: 0.8em;
  vertical-align: 0.1em;
}

/* ---------- notation cast ---------- */
.cast-grid {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  gap: 16px;
  margin-top: 26px;
}
@media (max-width: 640px) {
  .cast-grid { grid-template-columns: repeat(2, 1fr); }
}
.cast-card {
  background: var(--card);
  border: 1px solid var(--card-border);
  border-radius: var(--radius);
  padding: 18px;
  text-align: center;
  opacity: 0;
  transform: translateY(18px) scale(0.96);
  transition: opacity 0.5s ease, transform 0.5s ease;
  transition-delay: calc(var(--i) * 0.15s);
}
.cast-grid.in .cast-card { opacity: 1; transform: none; }
.cast-sym { font-size: 1.9rem; color: var(--accent3); line-height: 1.2; }
.cast-emoji { font-size: 1.5rem; margin: 4px 0; }
.cast-card h3 { margin: 4px 0 6px; font-size: 1rem; }
.cast-card p { margin: 0; color: var(--text-dim); font-size: 0.85rem; }

/* ---------- section 1 ---------- */
.flow-grid {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  gap: 12px;
}
.flow-grid figure { margin: 0; }
.flow-grid canvas {
  width: 100%;
  height: auto;
  display: block;
  border-radius: 10px;
  border: 1px solid var(--card-border);
}
.flow-grid figcaption {
  text-align: center;
  font-size: 0.8rem;
  color: var(--text-dim);
  margin-top: 4px;
}
@media (max-width: 640px) {
  .flow-grid { grid-template-columns: repeat(2, 1fr); }
}

/* ---------- section 3 ---------- */
.slider-grid {
  display: grid;
  grid-template-columns: repeat(2, 1fr);
  gap: 8px 28px;
  margin-top: 14px;
}
@media (max-width: 640px) {
  .slider-grid { grid-template-columns: 1fr; }
}
.slider-grid .slider-label { justify-content: space-between; }
.slider-grid .slider-label input[type="range"] { width: 55%; }
.slider-label.good { color: var(--good); }
.slider-label.bad { color: var(--bad); }

/* ---------- section 5 ---------- */
.derive-steps { display: flex; flex-direction: column; gap: 10px; }
.derive-line {
  border: 1px solid var(--card-border);
  border-radius: 12px;
  padding: 10px 16px;
  background: var(--bg-alt);
  opacity: 0.12;
  filter: grayscale(1);
  transition: opacity 0.5s ease, filter 0.5s ease, border-color 0.5s ease, box-shadow 0.5s ease;
}
.derive-line.shown { opacity: 0.6; filter: none; }
.derive-line.current {
  opacity: 1;
  border-color: var(--accent);
  box-shadow: 0 0 24px rgba(124, 155, 255, 0.15);
}
.derive-line p { margin: 0; color: var(--text-dim); font-size: 0.88rem; }
.derive-tag {
  font-size: 0.75rem;
  font-weight: 700;
  letter-spacing: 0.04em;
  text-transform: uppercase;
  color: var(--accent3);
}
.math-details { margin-top: 24px; }

/* ---------- section 7 ---------- */
.code-block {
  margin: 0;
  background: #05060d;
  border: 1px solid var(--card-border);
  border-radius: 10px;
  padding: 12px 0;
  overflow-x: auto;
  font-family: "SF Mono", Menlo, Consolas, monospace;
  font-size: 0.8rem;
  line-height: 1.75;
}
.code-line {
  display: block;
  white-space: pre;
  min-height: 1.75em;
  padding: 0 14px;
  color: var(--text-dim);
  border-left: 3px solid transparent;
  transition: background 0.3s ease, color 0.3s ease, border-color 0.3s ease;
}
.code-line.active {
  background: rgba(124, 155, 255, 0.14);
  border-left-color: var(--accent);
  color: var(--text);
}
.code-line .c { color: #6b7194; }
.loop-step em { color: var(--text-dim); font-style: normal; opacity: 0.8; }
.knob-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(220px, 1fr));
  gap: 16px;
  margin-top: 16px;
}
.knob-grid .why-card { margin-bottom: 0; }
.phase-grid > * { min-width: 0; }

.formula-hero {
  background: linear-gradient(135deg, #1c2044, #241a3a);
  border: 1px solid var(--card-border);
  border-radius: var(--radius);
  padding: 18px 24px;
  margin: 26px 0;
  text-align: center;
}
.formula-hero.small { padding: 12px 20px; }
.formula-hero-label {
  font-size: 0.75rem;
  font-weight: 700;
  letter-spacing: 0.06em;
  text-transform: uppercase;
  color: var(--accent3);
}
.formula-hero p { margin: 4px 0 0; color: var(--text-dim); font-size: 0.9rem; }

/* ---------- readouts / tug ---------- */
.readouts {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(130px, 1fr));
  gap: 10px;
  margin-top: 14px;
}
.readout {
  background: var(--bg-alt);
  border: 1px solid var(--card-border);
  border-radius: 10px;
  padding: 8px 12px;
  display: flex;
  flex-direction: column;
  gap: 2px;
}
.readout span { font-size: 0.75rem; color: var(--text-dim); }
.readout b { font-size: 1.05rem; font-variant-numeric: tabular-nums; color: var(--text); }

.tug { margin-top: 14px; display: flex; flex-direction: column; gap: 8px; }
.tug-row { display: grid; grid-template-columns: 190px 1fr; align-items: center; gap: 12px; }
@media (max-width: 640px) {
  .tug-row { grid-template-columns: 1fr; gap: 4px; }
}
.tug-label { font-size: 0.86rem; }
.tug-row.good .tug-label { color: var(--good); }
.tug-row.bad .tug-label { color: var(--bad); }
.tug-track {
  height: 14px;
  background: var(--bg-alt);
  border: 1px solid var(--card-border);
  border-radius: 999px;
  overflow: hidden;
}
.tug-bar { height: 100%; width: 50%; border-radius: 999px; transition: width 0.15s linear; }
.tug-row.good .tug-bar { background: linear-gradient(90deg, #2fb99a, var(--good)); }
.tug-row.bad .tug-bar { background: linear-gradient(90deg, #d4507f, var(--bad)); }

/* ---------- diffusion demo ---------- */
.diff-grid {
  display: grid;
  grid-template-columns: 90px repeat(3, 1fr);
  gap: 10px 12px;
  align-items: center;
}
.diff-head { font-size: 0.8rem; color: var(--text-dim); text-align: center; }
.diff-label { font-weight: 700; font-size: 0.9rem; }
.diff-cell { position: relative; }
.diff-canvas, .diff-cell canvas {
  width: 100%;
  height: auto;
  display: block;
  border-radius: 10px;
  border: 1px solid var(--card-border);
}
.same-badge {
  position: absolute;
  top: 6px;
  right: 6px;
  font-size: 0.68rem;
  font-weight: 700;
  background: rgba(11, 13, 23, 0.8);
  color: var(--accent3);
  border: 1px solid var(--accent3);
  border-radius: 999px;
  padding: 1px 8px;
}
@media (max-width: 640px) {
  .diff-grid { grid-template-columns: 60px repeat(3, 1fr); gap: 6px; }
  .diff-label { font-size: 0.72rem; }
}

[data-stage] { transition: opacity 0.5s ease, filter 0.5s ease; }
.diff-demo [data-stage].hidden-stage { opacity: 0.12; filter: grayscale(1); }

.stage-box {
  background: var(--bg-alt);
  border: 1px solid var(--card-border);
  border-radius: 12px;
  padding: 12px 16px;
  margin-top: 14px;
}
.stage-dots { display: flex; gap: 6px; margin-bottom: 6px; }
.stage-dots span {
  width: 9px;
  height: 9px;
  border-radius: 50%;
  background: var(--card-border);
  transition: background 0.3s ease;
}
.stage-dots span.on { background: var(--accent); }
.stage-text { margin: 0; color: var(--text); font-size: 0.95rem; min-height: 3em; }

.loss-table {
  width: 100%;
  border-collapse: collapse;
  margin-top: 14px;
  font-size: 0.9rem;
}
.loss-table th, .loss-table td {
  border: 1px solid var(--card-border);
  padding: 9px 12px;
  text-align: center;
}
.loss-table td:first-child { text-align: left; color: var(--text-dim); }
.loss-table th { background: var(--card); }
.result-line {
  margin-top: 10px;
  padding: 10px 14px;
  border-radius: 10px;
  background: rgba(110, 231, 200, 0.07);
  border: 1px solid rgba(110, 231, 200, 0.3);
  font-size: 0.93rem;
  overflow-x: auto;
}

/* ---------- gotchas / refs ---------- */
.gotcha-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(280px, 1fr));
  gap: 16px;
  margin-top: 26px;
}
.gotcha-grid .why-card { margin-bottom: 0; }

.math-content > p { color: var(--text-dim); }
.derivation-step .katex-display { color: var(--text); }
.nowrap { white-space: nowrap; }

.refs {
  margin-top: 50px;
  background: var(--card);
  border: 1px solid var(--card-border);
  border-radius: var(--radius);
  padding: 18px 24px;
}
.refs h3 { margin: 0 0 8px; font-size: 1.05rem; }
.refs ul { margin: 0; padding-left: 20px; color: var(--text-dim); font-size: 0.92rem; }
.refs li { margin: 4px 0; }

@media (max-width: 640px) {
  .topnav { padding: 10px 16px; }
  .topnav .links {
    flex-wrap: nowrap;
    overflow-x: auto;
    width: 100%;
    gap: 14px;
    scrollbar-width: none;
  }
  .topnav .links::-webkit-scrollbar { display: none; }
  .topnav .links a { white-space: nowrap; }
}

@media (prefers-reduced-motion: reduce) {
  .cast-card { opacity: 1; transform: none; transition: none; }
  .scroll-cue, .judge.thinking .judge-emoji { animation: none; }
  .reveal { transition: none; }
}