/* ==========================================================================
   rfpaavpt.com — RFPA · AVPT — the mathematics of Odisena
   Austere, paper-like, math-first. Shares the Odisena constellation's
   warm-paper / dark-ink design tokens (see odisena.com/systems).
   ========================================================================== */

/* --------------------------------------------------------------------------
   Production-safe font fallbacks (no dependencies, pure CSS).
   If the Fontshare/Google CDN fails, these metric-adjusted system fallbacks
   keep the type hierarchy intact and minimize layout shift.
   -------------------------------------------------------------------------- */
@font-face {
  font-family: 'Zodiak Fallback';
  src: local('Georgia'), local('Times New Roman'), local('serif');
  size-adjust: 102%;
  ascent-override: 92%;
  descent-override: 24%;
  line-gap-override: 0%;
}
@font-face {
  font-family: 'Satoshi Fallback';
  src: local('Segoe UI'), local('Helvetica Neue'), local('Arial'), local('sans-serif');
  size-adjust: 100%;
  ascent-override: 96%;
  descent-override: 24%;
  line-gap-override: 0%;
}
@font-face {
  font-family: 'JetBrains Mono Fallback';
  src: local('SFMono-Regular'), local('Menlo'), local('Consolas'), local('monospace');
  size-adjust: 100%;
}

:root {
  /* Paper / ink foundation (light) */
  --paper: #f4ede0;
  --paper-2: #ece3d3;
  --paper-3: #e3d8c4;
  --ink: #1b1712;
  --ink-2: #4a4238;
  --ink-3: #746a5b;
  --hairline: #cdbfa6;
  --hairline-strong: #b3a58a;

  /* Electric signal — a single accent, used sparingly */
  --signal: #d8461f;
  --signal-ink: #ffffff;
  --signal-soft: rgba(216, 70, 31, 0.10);

  /* Label hues — literal block labels, restrained, mono-adjacent */
  --lb-definition: #2f5f8a;
  --lb-invariant: #296035;
  --lb-doctrine: #5f4a8a;
  --lb-boundary: #8a2f2f;

  /* Type */
  --font-display: 'Zodiak', 'Zodiak Fallback', 'Georgia', serif;
  --font-body: 'Satoshi', 'Satoshi Fallback', 'Inter', system-ui, sans-serif;
  --font-mono: 'JetBrains Mono', 'JetBrains Mono Fallback', ui-monospace, 'SFMono-Regular', monospace;

  --text-xs: 0.75rem;
  --text-sm: 0.875rem;
  --text-base: 1rem;
  --text-lg: 1.1875rem;
  --text-xl: 1.5rem;
  --text-2xl: 2.125rem;
  --text-3xl: 3rem;
  --text-hero: clamp(2.5rem, 6vw, 4.75rem);

  --sp-1: 0.25rem; --sp-2: 0.5rem; --sp-3: 0.75rem; --sp-4: 1rem;
  --sp-6: 1.5rem; --sp-8: 2rem; --sp-12: 3rem; --sp-16: 4rem;
  --sp-24: 6rem; --sp-32: 8rem;

  --maxw: 1120px;
  --gutter: clamp(1.25rem, 4vw, 4rem);
  --radius: 3px;

  --bg: var(--paper);
  --bg-2: var(--paper-2);
  --bg-3: var(--paper-3);
  --fg: var(--ink);
  --fg-2: var(--ink-2);
  --fg-3: var(--ink-3);
  --line: var(--hairline);

  color-scheme: light;
}

/* Dark mode — dark ink foundation with warm paper accents */
@media (prefers-color-scheme: dark) {
  :root {
    --bg: #14110d;
    --bg-2: #1c1813;
    --bg-3: #26211a;
    --fg: #f4ede0;
    --fg-2: #cabca6;
    --fg-3: #9b8f7c;
    --line: #3a3227;
    --signal: #ff5b2e;
    --signal-ink: #14110d;
    --signal-soft: rgba(255, 91, 46, 0.14);
    --lb-definition: #6fa8dc;
    --lb-invariant: #6fbf82;
    --lb-doctrine: #ab96d9;
    --lb-boundary: #e08a8a;
    color-scheme: dark;
  }
}

* { box-sizing: border-box; }

html { -webkit-text-size-adjust: 100%; scroll-behavior: smooth; overflow-x: hidden; }
@media (prefers-reduced-motion: reduce) {
  html { scroll-behavior: auto; }
  *, *::before, *::after {
    animation-duration: 0.001ms !important;
    animation-iteration-count: 1 !important;
    transition-duration: 0.001ms !important;
  }
}

body {
  margin: 0;
  background: var(--bg);
  color: var(--fg);
  font-family: var(--font-body);
  font-size: var(--text-base);
  line-height: 1.65;
  -webkit-font-smoothing: antialiased;
  text-rendering: optimizeLegibility;
}

/* Paper grain / grid texture — subtle, drawn not imaged */
body::before {
  content: '';
  position: fixed;
  inset: 0;
  pointer-events: none;
  z-index: 0;
  background-image:
    linear-gradient(to right, var(--line) 1px, transparent 1px),
    linear-gradient(to bottom, var(--line) 1px, transparent 1px);
  background-size: 88px 88px;
  opacity: 0.10;
}
@media (prefers-color-scheme: dark) {
  body::before { opacity: 0.16; }
}

h1, h2, h3, h4 {
  font-family: var(--font-display);
  font-weight: 500;
  line-height: 1.12;
  letter-spacing: -0.01em;
  margin: 0 0 var(--sp-4);
  color: var(--fg);
}
h1 { font-size: var(--text-3xl); }
h2 { font-size: var(--text-2xl); }
h3 { font-size: var(--text-xl); }
p { margin: 0 0 var(--sp-4); max-width: 68ch; }

a { color: var(--fg); text-decoration: underline; text-decoration-color: var(--line); text-underline-offset: 3px; }
a:hover { color: var(--signal); text-decoration-color: currentColor; }

.mono {
  font-family: var(--font-mono);
  font-size: var(--text-xs);
  letter-spacing: 0.04em;
  text-transform: uppercase;
  color: var(--fg-3);
}

/* Layout primitives */
.shell { position: relative; z-index: 1; }
.wrap { max-width: var(--maxw); margin: 0 auto; padding: 0 var(--gutter); }
.section { padding: var(--sp-24) 0; }
.section--tight { padding: var(--sp-16) 0; }
.rule { border: 0; border-top: 1px solid var(--line); margin: 0; }

/* Eyebrow / kicker */
.kicker {
  font-family: var(--font-mono);
  font-size: var(--text-xs);
  letter-spacing: 0.16em;
  text-transform: uppercase;
  color: var(--signal);
  display: inline-flex;
  align-items: center;
  gap: var(--sp-2);
  margin-bottom: var(--sp-4);
}
.kicker::before {
  content: '';
  width: 22px; height: 1px; background: var(--signal); display: inline-block;
}

/* Skip link */
:focus-visible {
  outline: 2px solid var(--signal);
  outline-offset: 3px;
  border-radius: 2px;
}
.skip-link {
  position: absolute; left: var(--sp-4); top: -60px; z-index: 100;
  background: var(--signal); color: var(--signal-ink);
  padding: var(--sp-2) var(--sp-4); border-radius: var(--radius);
  transition: top 0.2s;
  text-decoration: none;
}
.skip-link:focus { top: var(--sp-2); color: var(--signal-ink); }

/* ---- Header ---- */
.topbar {
  position: sticky; top: 0; z-index: 50;
  background: color-mix(in srgb, var(--bg) 88%, transparent);
  backdrop-filter: blur(8px);
  border-bottom: 1px solid var(--line);
}
.topbar__inner {
  display: flex; align-items: center; justify-content: space-between;
  gap: var(--sp-6); height: 64px;
}
.wordmark { display: inline-flex; align-items: center; gap: var(--sp-3); color: var(--fg); text-decoration: none; }
.wordmark .mark { color: var(--fg); flex: none; }
.wordmark__text {
  font-family: var(--font-display); font-size: 1.2rem; font-weight: 600;
  letter-spacing: -0.01em;
}
.topbar__tools { display: flex; align-items: center; gap: var(--sp-4); }
.topbar__tools a { font-family: var(--font-mono); font-size: var(--text-xs); letter-spacing: 0.06em; text-transform: uppercase; color: var(--fg-2); text-decoration: none; }
.topbar__tools a:hover { color: var(--signal); }

/* ---- Hero ---- */
.hero { padding: var(--sp-24) 0 var(--sp-16); position: relative; }
.hero h1 { font-size: var(--text-hero); font-weight: 500; max-width: 20ch; }
.hero__lede { font-size: var(--text-lg); color: var(--fg-2); max-width: 62ch; margin-top: var(--sp-6); }
.hero__meta {
  display: flex; flex-wrap: wrap; gap: var(--sp-6); margin-top: var(--sp-8);
  padding-top: var(--sp-6); border-top: 1px solid var(--line);
}
.hero__meta .mono { color: var(--fg-3); }

/* ---- Page structure ---- */
.crumb { font-family: var(--font-mono); font-size: var(--text-xs); color: var(--fg-3); margin-bottom: var(--sp-4); }
.crumb a { color: var(--fg-3); }
.crumb a:hover { color: var(--signal); }

.section-num {
  font-family: var(--font-mono); font-size: var(--text-xs); letter-spacing: 0.1em;
  text-transform: uppercase; color: var(--fg-3); margin-bottom: var(--sp-2); display: block;
}

/* ---- Literal labeled math blocks ---- */
.block {
  border: 1px solid var(--line);
  border-left: 3px solid var(--fg-3);
  border-radius: var(--radius);
  background: var(--bg-2);
  padding: var(--sp-6) var(--sp-8);
  margin: var(--sp-8) 0;
}
.block[data-label='definition'] { border-left-color: var(--lb-definition); }
.block[data-label='invariant'] { border-left-color: var(--lb-invariant); }
.block[data-label='doctrine'] { border-left-color: var(--lb-doctrine); }
.block[data-label='boundary'] { border-left-color: var(--lb-boundary); background: color-mix(in srgb, var(--lb-boundary) 8%, var(--bg-2)); }

.block__label {
  font-family: var(--font-mono); font-size: var(--text-xs); letter-spacing: 0.12em;
  text-transform: uppercase; display: inline-flex; align-items: center; gap: var(--sp-2);
  margin-bottom: var(--sp-3); font-weight: 500;
}
.block[data-label='definition'] .block__label { color: var(--lb-definition); }
.block[data-label='invariant'] .block__label { color: var(--lb-invariant); }
.block[data-label='doctrine'] .block__label { color: var(--lb-doctrine); }
.block[data-label='boundary'] .block__label { color: var(--lb-boundary); }
.block__label::before { content: ''; width: 6px; height: 6px; border-radius: 50%; background: currentColor; flex: none; }
.block__num { color: var(--fg-3); font-weight: 400; }

.block h3 { font-size: var(--text-lg); margin-bottom: var(--sp-3); }
.block p:last-child { margin-bottom: 0; }
.block .katex-display { margin: var(--sp-4) 0; overflow-x: auto; overflow-y: hidden; padding-bottom: 2px; }
.block .katex { font-size: 1.05em; }

/* Statement / prose separation inside a block */
.block__stmt { margin-top: var(--sp-4); }
.block__note { font-size: var(--text-sm); color: var(--fg-3); margin-top: var(--sp-4); margin-bottom: 0; }

/* ---- Definition list / spec table ---- */
.spec { width: 100%; border-collapse: collapse; margin: var(--sp-6) 0; }
.spec th, .spec td {
  text-align: left; padding: var(--sp-3) var(--sp-4);
  border-top: 1px solid var(--line); vertical-align: top; font-size: var(--text-sm);
}
.spec th { font-family: var(--font-mono); font-size: var(--text-xs); text-transform: uppercase;
  letter-spacing: 0.06em; color: var(--fg-3); font-weight: 500; width: 30%; }
.table-scroll { max-width: 100%; overflow-x: auto; -webkit-overflow-scrolling: touch; }
.table-scroll > .spec { min-width: 480px; }

/* ---- Fine-line diagrams ---- */
.diagram { width: 100%; height: auto; color: var(--fg); margin: var(--sp-6) 0; }
.diagram .d-line { stroke: var(--line); stroke-width: 1; fill: none; }
.diagram .d-arc { stroke: var(--signal); stroke-width: 1.5; fill: none; }
.diagram .d-node { fill: var(--bg); stroke: var(--fg); stroke-width: 1.2; }
.diagram text { font-family: var(--font-mono); font-size: 11px; fill: var(--fg); }
.diagram .d-sub { fill: var(--fg-3); font-size: 9px; }
.diagram .d-dashed { stroke-dasharray: 4 5; }

/* ---- Layout helpers ---- */
.two-col { display: grid; grid-template-columns: 0.85fr 1.15fr; gap: var(--sp-16); align-items: start; }
.stack > * + * { margin-top: var(--sp-4); }
.flow > * + * { margin-top: var(--sp-6); }
.muted { color: var(--fg-3); }

/* ---- Grid of small cells (media categories / lanes) ---- */
.grid { display: grid; gap: 1px; background: var(--line); border: 1px solid var(--line); }
.grid--4 { grid-template-columns: repeat(4, 1fr); }
.grid--3 { grid-template-columns: repeat(3, 1fr); }
.cell {
  background: var(--bg); padding: var(--sp-5) var(--sp-6);
  display: flex; flex-direction: column; gap: var(--sp-2);
}
.cell__idx { font-family: var(--font-mono); font-size: var(--text-xs); color: var(--fg-3); }
.cell h4 { margin: 0; font-family: var(--font-display); font-size: var(--text-base); font-weight: 600; }
.cell p { margin: 0; color: var(--fg-2); font-size: var(--text-sm); }

/* ---- Notice / boundary callout ---- */
.notice {
  border-width: 2px;
  border-left-width: 5px;
  background: color-mix(in srgb, var(--lb-boundary) 10%, var(--bg));
  padding: var(--sp-8);
  font-size: var(--text-base);
}
.notice .block__label { font-size: var(--text-sm); }
.notice h3 { font-family: var(--font-body); font-size: var(--text-base); font-weight: 700; margin-bottom: var(--sp-2); color: var(--lb-boundary); }

/* ---- Colophon ---- */
.colophon {
  border-top: 1px solid var(--line);
  padding-top: var(--sp-8);
}
.colophon p { color: var(--fg-2); }

/* ---- Footer ---- */
.footer { border-top: 1px solid var(--line); padding: var(--sp-12) 0; background: var(--bg-2); }
.footer__row { display: flex; justify-content: space-between; align-items: center; gap: var(--sp-4); flex-wrap: wrap; }
.footer a { color: var(--fg-2); font-size: var(--text-sm); }
.footer a:hover { color: var(--signal); }

.chip {
  font-family: var(--font-mono); font-size: 0.68rem; letter-spacing: 0.06em;
  text-transform: uppercase; padding: 3px 8px; border-radius: 999px;
  border: 1px solid currentColor; display: inline-flex; align-items: center; gap: 5px;
  white-space: nowrap; color: var(--fg-3);
}
.chip::before { content: ''; width: 6px; height: 6px; border-radius: 50%; background: currentColor; }

/* ---- 404 ---- */
.fourohfour { min-height: 70vh; display: flex; align-items: center; }
.fourohfour__big { font-family: var(--font-mono); font-size: clamp(4rem, 14vw, 9rem); color: var(--signal); line-height: 1; }

/* ---- Responsive ---- */
@media (max-width: 900px) {
  .two-col { grid-template-columns: 1fr; gap: var(--sp-8); }
  .grid--4 { grid-template-columns: repeat(2, 1fr); }
  .grid--3 { grid-template-columns: 1fr; }
  .footer__row { flex-direction: column; align-items: flex-start; }
}
@media (max-width: 640px) {
  .grid--4, .grid--2 { grid-template-columns: 1fr; }
  .section { padding: var(--sp-16) 0; }
  .hero { padding: var(--sp-16) 0 var(--sp-12); }
  .block { padding: var(--sp-5) var(--sp-5); }
}

@media print {
  .topbar { position: static; }
}