/* π₀.5 Standalone Site — design system
   warm-dark single-surface · serif prose · contractual color palette */

:root {
  /* Surface */
  --bg:           #15161a;
  --bg-fig:       #1a1c20;
  --rule:         #2a2c33;
  --rule-strong:  #3a3c43;

  /* Prose */
  --ink:          #e8e4d8;
  --ink-strong:   #ffffff;
  --ink-muted:    #9b968a;
  --ink-dim:      #6b6961;

  /* Link */
  --link:         #ffd866;
  --link-soft:    rgba(255, 216, 102, 0.18);

  /* Contractual viz palette — same meaning across every figure */
  --c-vlm:        #b48cff;  /* VLM / language tokens / image patches in VLM */
  --c-action:     #ffa84d;  /* action expert / action tokens / action chunk */
  --c-flow:       #5eead4;  /* flow-matching velocity / ODE step / gradients-that-flow */
  --c-fast:       #ff7a8a;  /* FAST / discrete / autoregressive */
  --c-grad-stop:  #ff5252;  /* stop-gradient bar / blocked path */
  --c-grad-flow:  #5eead4;  /* gradients that pass — same as flow on purpose */
  --c-frozen:     #6b7280;  /* frozen weights */
  --c-trained:    #a3e635;  /* trained / receiving updates */
  --c-noise:      #4a4d56;  /* Gaussian noise, pre-denoise */
  --c-data:       #ffd866;  /* clean data target — matches link color on purpose */

  /* Joint traces (D=7) */
  --j0: #ef4444; --j1: #f59e0b; --j2: #84cc16; --j3: #22d3ee;
  --j4: #818cf8; --j5: #ec4899; --j6: #f87171;

  /* Type */
  --font-prose: 'Source Serif 4', 'Source Serif Pro', Charter, Georgia, serif;
  --font-ui:    'Inter', -apple-system, BlinkMacSystemFont, system-ui, sans-serif;
  --font-mono:  'JetBrains Mono', ui-monospace, 'SF Mono', Menlo, monospace;

  --fs-xs:   0.722rem;  /* 13 */
  --fs-sm:   0.833rem;  /* 15 */
  --fs-base: 1rem;      /* 18 */
  --fs-md:   1.166rem;  /* 21 */
  --fs-lg:   1.444rem;  /* 26 */
  --fs-xl:   1.777rem;  /* 32 */
  --fs-2xl:  2.444rem;  /* 44 */

  --lh-prose: 1.65;
  --lh-tight: 1.18;
  --lh-ui:    1.40;

  /* Layout */
  --w-prose:       38rem;
  --w-figure:      56rem;
  --w-figure-wide: 72rem;
}

* { box-sizing: border-box; }
html { font-size: 18px; }
body {
  background: var(--bg);
  color: var(--ink);
  font-family: var(--font-prose);
  font-size: var(--fs-base);
  line-height: var(--lh-prose);
  margin: 0;
  -webkit-font-smoothing: antialiased;
  text-rendering: optimizeLegibility;
}

/* ── Headings ─────────────────────────────────────────────── */
h1, h2, h3, h4 {
  font-family: var(--font-ui);
  color: var(--ink-strong);
  line-height: var(--lh-tight);
  font-weight: 600;
  margin: 0 0 0.5rem 0;
  max-width: var(--w-prose);
  margin-left: auto;
  margin-right: auto;
}
h1 { font-size: var(--fs-2xl); font-weight: 700; }
h2 { font-size: var(--fs-xl); margin-top: 4rem; }
h3 { font-size: var(--fs-lg); margin-top: 2.5rem; }
h4 { font-size: var(--fs-md); margin-top: 1.5rem; font-weight: 500; }

.eyebrow {
  display: block;
  font-family: var(--font-ui);
  font-size: var(--fs-xs);
  font-weight: 500;
  letter-spacing: 0.12em;
  text-transform: uppercase;
  color: var(--link);
  margin: 0 auto 0.5rem;
  max-width: var(--w-prose);
}

.lede {
  font-family: var(--font-prose);
  font-size: var(--fs-md);
  font-style: italic;
  color: var(--ink);
  line-height: 1.55;
  max-width: var(--w-prose);
  margin: 0 auto 2rem;
}

/* ── Prose ────────────────────────────────────────────────── */
.prose {
  max-width: var(--w-prose);
  margin: 0 auto 1.5rem;
}
.prose p { margin: 0 0 1.25rem; }
.prose strong { color: var(--ink-strong); font-weight: 700; }
.prose em { color: var(--ink); font-style: italic; }
.prose code {
  font-family: var(--font-mono);
  font-size: 0.92em;
  background: rgba(255,255,255,0.06);
  padding: 0.05em 0.35em;
  border-radius: 3px;
}
.prose ul, .prose ol { padding-left: 1.5rem; margin: 0 0 1.25rem; }
.prose li { margin-bottom: 0.5rem; }

a {
  color: var(--link);
  text-decoration: none;
  border-bottom: 1px solid var(--link-soft);
  transition: border-color 200ms ease;
}
a:hover { border-bottom-color: var(--link); }
a:focus-visible { outline: 2px solid var(--link); outline-offset: 2px; }

/* ── Page chrome ──────────────────────────────────────────── */
.page-header {
  height: 56px;
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: 0 clamp(1rem, 4vw, 2rem);
  border-bottom: 1px solid var(--rule);
  font-family: var(--font-mono);
  font-size: 14px;
}
.page-header .mark {
  color: var(--ink-strong);
  font-weight: 600;
  border: none;
  text-decoration: none;
}
.page-header .mark:hover { color: var(--link); border: none; }
.progress-strip {
  display: flex;
  gap: 8px;
  font-family: var(--font-ui);
  font-size: var(--fs-xs);
  color: var(--ink-muted);
  align-items: center;
}
.progress-strip .seg {
  width: 26px; height: 2px;
  background: var(--rule-strong);
  border: none;
  padding: 0;
  display: inline-block;
}
.progress-strip .seg.current { background: var(--link); }
.progress-strip a { border: none; }

main {
  padding-inline: clamp(1rem, 4vw, 2rem);
  padding-block: 3rem 6rem;
}
section { margin-bottom: 4rem; }

/* ── Figures ──────────────────────────────────────────────── */
figure {
  margin: 2rem auto 2.5rem;
  max-width: var(--w-figure);
}
figure.wide { max-width: var(--w-figure-wide); }
figure.bleed { max-width: 100%; }

.fig-label {
  display: block;
  font-family: var(--font-ui);
  font-size: var(--fs-xs);
  letter-spacing: 0.12em;
  text-transform: uppercase;
  color: var(--ink-muted);
  margin-bottom: 0.5rem;
}
.fig-body {
  background: var(--bg-fig);
  padding: 1.5rem;
  border-radius: 4px;
  position: relative;
}
figcaption {
  font-family: var(--font-prose);
  font-size: var(--fs-sm);
  font-style: italic;
  color: var(--ink-muted);
  max-width: 36rem;
  margin: 1rem auto 0;
  line-height: 1.55;
  text-align: left;
}
.fig-controls {
  border-top: 1px solid var(--rule);
  padding-top: 1rem;
  margin-top: 1rem;
  display: flex;
  flex-wrap: wrap;
  gap: 1rem 1.5rem;
  align-items: center;
  font-family: var(--font-ui);
  font-size: var(--fs-sm);
  color: var(--ink-muted);
}
.fig-controls label { display: inline-flex; align-items: center; gap: 0.5rem; }
.fig-controls input[type="range"] {
  accent-color: var(--link);
  vertical-align: middle;
  min-width: 140px;
}
.fig-controls .readout {
  font-family: var(--font-mono);
  font-variant-numeric: tabular-nums;
  color: var(--ink);
  min-width: 4ch;
  display: inline-block;
}
.fig-controls button {
  font-family: var(--font-ui);
  font-size: var(--fs-sm);
  background: transparent;
  color: var(--ink);
  border: 1px solid var(--rule-strong);
  padding: 0.35rem 0.85rem;
  border-radius: 4px;
  cursor: pointer;
  transition: all 150ms ease;
}
.fig-controls button:hover { background: rgba(255,255,255,0.05); border-color: var(--ink-muted); }
.fig-controls button.active {
  background: var(--ink-strong);
  color: var(--bg);
  border-color: var(--ink-strong);
}

.legend {
  display: flex;
  flex-wrap: wrap;
  gap: 1rem 1.25rem;
  font-family: var(--font-ui);
  font-size: var(--fs-xs);
  color: var(--ink-muted);
  margin-top: 0.75rem;
  padding-top: 0.75rem;
  border-top: 1px solid var(--rule);
}
.legend .swatch {
  display: inline-block;
  width: 10px; height: 10px;
  border-radius: 2px;
  margin-right: 6px;
  vertical-align: middle;
}

/* ── Equations ────────────────────────────────────────────── */
.katex { font-size: 1.05em !important; }
.katex-display { margin: 1.5rem 0 !important; }
.katex-display > .katex { font-size: 1.15em !important; }
.eq-label {
  font-family: var(--font-ui);
  font-size: var(--fs-xs);
  letter-spacing: 0.12em;
  text-transform: uppercase;
  color: var(--ink-muted);
  text-align: center;
  margin-top: 1rem;
}

/* ── Sidenotes ────────────────────────────────────────────── */
.sn-anchor {
  font-family: var(--font-ui);
  font-size: 0.7em;
  vertical-align: super;
  color: var(--link);
  border: none;
  cursor: help;
}
@media (min-width: 1100px) {
  .has-sidenotes { position: relative; }
  .sidenote {
    position: absolute;
    right: -16rem;
    width: 14rem;
    font-family: var(--font-ui);
    font-size: var(--fs-xs);
    color: var(--ink-muted);
    line-height: 1.5;
    margin-top: 0.25rem;
  }
}
@media (max-width: 1099px) {
  .sidenote {
    display: block;
    font-family: var(--font-prose);
    font-style: italic;
    font-size: var(--fs-sm);
    color: var(--ink-muted);
    border-left: 2px solid var(--rule-strong);
    padding-left: 1rem;
    margin: 1rem auto;
    max-width: var(--w-prose);
  }
}

/* ── Details / collapsibles ───────────────────────────────── */
details {
  background: rgba(255,255,255,0.025);
  border-left: 2px solid var(--rule-strong);
  padding: 0.75rem 1rem;
  margin: 1.5rem auto;
  max-width: var(--w-prose);
  font-size: var(--fs-sm);
}
details summary {
  cursor: pointer;
  font-family: var(--font-ui);
  font-weight: 500;
  color: var(--ink-muted);
  outline: none;
  list-style: none;
}
details summary::before {
  content: '▸ ';
  color: var(--ink-dim);
  margin-right: 0.25rem;
}
details[open] summary::before { content: '▾ '; }
details[open] summary { color: var(--ink); margin-bottom: 0.75rem; }

/* ── Reveal motion ────────────────────────────────────────── */
.reveal {
  opacity: 0;
  transform: translateY(8px);
  transition: opacity 600ms cubic-bezier(0.2, 0.7, 0.2, 1),
              transform 600ms cubic-bezier(0.2, 0.7, 0.2, 1);
}
.reveal.is-revealed { opacity: 1; transform: translateY(0); }
.reveal-eq {
  opacity: 0;
  transition: opacity 600ms ease;
  transition-delay: 300ms;
}
.reveal-eq.is-revealed { opacity: 1; }

@media (prefers-reduced-motion: reduce) {
  .reveal, .reveal-eq { opacity: 1; transform: none; transition: none; }
}

/* ── Hero / index ─────────────────────────────────────────── */
.hero {
  max-width: var(--w-figure);
  margin: 4rem auto 5rem;
  padding-inline: clamp(1rem, 4vw, 2rem);
}
.hero h1 {
  font-size: clamp(2.25rem, 5.5vw, 3.5rem);
  line-height: 1.05;
  margin: 0 auto 2rem;
  max-width: 22ch;
  letter-spacing: -0.01em;
}
.hero .thesis {
  font-family: var(--font-prose);
  font-size: var(--fs-md);
  font-style: italic;
  color: var(--ink);
  max-width: 38rem;
  line-height: 1.55;
  margin: 0 auto;
}

/* ── TOC ──────────────────────────────────────────────────── */
.toc { max-width: var(--w-prose); margin: 2rem auto; }
.toc-item {
  display: block;
  padding: 1.25rem 0;
  border-bottom: 1px solid var(--rule);
  border-left: none;
  color: inherit;
  text-decoration: none;
}
.toc-item:hover { background: rgba(255,255,255,0.025); }
.toc-item:first-child { border-top: 1px solid var(--rule); }
.toc-item .num {
  font-family: var(--font-mono);
  font-size: var(--fs-sm);
  color: var(--ink-muted);
  margin-right: 1.5rem;
}
.toc-item .title {
  font-family: var(--font-ui);
  font-size: var(--fs-md);
  color: var(--ink-strong);
  font-weight: 600;
}
.toc-item .duration {
  font-family: var(--font-mono);
  color: var(--ink-dim);
  font-size: var(--fs-xs);
  margin-left: 1rem;
  letter-spacing: 0.05em;
}
.toc-item .desc {
  display: block;
  font-style: italic;
  color: var(--ink-muted);
  margin-top: 0.4rem;
  margin-left: 4.5ch;
  font-size: var(--fs-sm);
  font-family: var(--font-prose);
}

/* ── Footer / next ────────────────────────────────────────── */
.page-footer {
  border-top: 1px solid var(--rule);
  padding: 2.5rem clamp(1rem, 4vw, 2rem);
  font-family: var(--font-ui);
  font-size: var(--fs-xs);
  color: var(--ink-dim);
  display: flex;
  justify-content: space-between;
  align-items: flex-start;
  flex-wrap: wrap;
  gap: 2rem;
}
.page-footer .sources { max-width: 36rem; line-height: 1.55; }
.page-footer a.next {
  color: var(--link);
  border: none;
  font-family: var(--font-ui);
  font-size: var(--fs-sm);
  font-weight: 500;
  white-space: nowrap;
}

/* ── Canvas/SVG hosts ─────────────────────────────────────── */
.viz-canvas, .viz-svg {
  display: block;
  width: 100%;
  height: auto;
  max-width: 100%;
}

/* ── Mobile ───────────────────────────────────────────────── */
@media (max-width: 760px) {
  html { font-size: 17px; }
  h1 { font-size: 2rem; }
  h2 { font-size: 1.5rem; }
  h3 { font-size: 1.25rem; }
  .hero h1 { font-size: 2rem; }
  .fig-body { padding: 1rem; }
  .toc-item .desc { margin-left: 0; }
}