/* =====================================================================
 * main.css — The Atlas of Algorithms : the one design system
 * ---------------------------------------------------------------------
 * Dependency-free. A single, dark, typographic system. Color is rare and
 * carries meaning: the invariant/guarantee region, the active comparison,
 * the cost numbers. Monospace for code and counters; a humanist sans for
 * prose. Entries must use only these classes and tokens — the engine
 * (lib/algo.js) reads several of the custom properties below so draw()
 * can paint on-canvas in the same palette.
 *
 * Token map (the contract algo.js.readTheme() reads):
 *   --bg --panel --ink --muted --grid --accent --invariant --warn --cost
 *   --font-mono
 * ===================================================================== */

/* ----------------------------- Tokens ------------------------------- */
:root {
  /* Palette — dark, calm. Color used sparingly, for meaning. */
  --bg:        #0f1117;   /* page background */
  --panel:     #161922;   /* raised surfaces: stage, rail, code blocks */
  --panel-2:   #1c202c;   /* secondary surface: inputs, cards */
  --line:      #262b38;   /* hairline borders */
  --grid:      #262b38;   /* on-canvas gridlines (engine reads this) */
  --ink:       #e7e9ee;   /* primary text */
  --muted:     #9aa3b2;   /* secondary text, labels */
  --faint:     #828b9b;   /* tertiary text, captions — WCAG AA (≥4.5:1 on bg & panel-2) */

  /* Meaningful color. Each hue means one thing across the whole atlas. */
  --accent:    #6ea8fe;   /* MOTION: the active element / current comparison */
  --invariant: #3ddc97;   /* GUARANTEE: the invariant region / proven envelope */
  --cost:      #c792ea;   /* COST: operation counts, growth */
  --warn:      #f4a259;   /* attention: degenerate input, worst case, errors */
  --accent-dim: rgba(110, 168, 254, 0.16);
  --invariant-dim: rgba(61, 220, 151, 0.14);

  /* Type. Serif/humanist for prose; mono for code, counters, controls. */
  --font-prose: ui-serif, Georgia, "Iowan Old Style", "Palatino Linotype", serif;
  --font-sans:  ui-sans-serif, system-ui, -apple-system, "Segoe UI", Roboto, sans-serif;
  --font-mono:  ui-monospace, SFMono-Regular, Menlo, Consolas, "Liberation Mono", monospace;

  --fs-xs:   0.78rem;
  --fs-sm:   0.875rem;
  --fs-base: 1rem;
  --fs-lg:   1.2rem;
  --fs-xl:   1.6rem;
  --fs-2xl:  2.4rem;
  --leading: 1.65;

  /* Spacing scale */
  --sp-1: 0.25rem;
  --sp-2: 0.5rem;
  --sp-3: 0.75rem;
  --sp-4: 1rem;
  --sp-5: 1.5rem;
  --sp-6: 2rem;
  --sp-8: 3rem;
  --sp-10: 4rem;

  --radius: 10px;
  --radius-sm: 6px;
  --measure: 68ch;        /* readable prose line length */
  --maxw: 1100px;
  --shadow: 0 1px 0 rgba(255,255,255,0.02), 0 8px 24px rgba(0,0,0,0.35);
}

/* --------------------------- Reset / base --------------------------- */
*, *::before, *::after { box-sizing: border-box; }

html { -webkit-text-size-adjust: 100%; }

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

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

code, pre, kbd, samp { font-family: var(--font-mono); }

::selection { background: var(--accent-dim); }

:focus-visible {
  outline: 2px solid var(--accent);
  outline-offset: 2px;
  border-radius: var(--radius-sm);
}

/* --------------------------- Page shell ----------------------------- */
.page {
  max-width: var(--maxw);
  margin: 0 auto;
  padding: var(--sp-6) var(--sp-5) var(--sp-10);
}

/* --------------------------- Breadcrumb ----------------------------- */
.crumb {
  font-family: var(--font-mono);
  font-size: var(--fs-xs);
  letter-spacing: 0.02em;
  color: var(--faint);
  margin-bottom: var(--sp-5);
}
.crumb a { color: var(--muted); }
.crumb a:hover { color: var(--ink); }
.crumb .sep { margin: 0 var(--sp-2); color: var(--line); }

/* --------------------------- Entry head ----------------------------- */
.entry-head { margin-bottom: var(--sp-6); }
.entry-head .family {
  display: inline-block;
  font-family: var(--font-mono);
  font-size: var(--fs-xs);
  text-transform: uppercase;
  letter-spacing: 0.12em;
  color: var(--accent);
  margin-bottom: var(--sp-2);
}
.entry-head h1 {
  font-family: var(--font-prose);
  font-weight: 600;
  font-size: var(--fs-2xl);
  line-height: 1.1;
  margin: 0 0 var(--sp-2);
  letter-spacing: -0.01em;
}
.entry-head .one-liner {
  font-family: var(--font-prose);
  font-size: var(--fs-lg);
  color: var(--muted);
  margin: 0;
  max-width: var(--measure);
}

/* ============================== STAGE =============================== *
 * The figure: canvas container (responsive) + annotation + caption.
 * ==================================================================== */
.stage-figure {
  margin: 0 0 var(--sp-5);
}

#stage {
  position: relative;
  width: 100%;
  /* A pleasant default canvas height; entries may override via inline
   * style or a modifier class. The engine reads the rendered height. */
  height: clamp(260px, 42vw, 460px);
  background: var(--panel);
  border: 1px solid var(--line);
  border-radius: var(--radius);
  box-shadow: var(--shadow);
  overflow: hidden;
}

.algo-canvas {
  display: block;
  width: 100%;
  height: 100%;
}

/* The invariant/guarantee annotation, surfaced by the engine. */
#annotation {
  font-family: var(--font-mono);
  font-size: var(--fs-sm);
  color: var(--invariant);
  background: var(--invariant-dim);
  border-left: 2px solid var(--invariant);
  padding: var(--sp-2) var(--sp-3);
  border-radius: var(--radius-sm);
  margin-top: var(--sp-3);
  min-height: 1.5em;
}

.stage-caption {
  font-size: var(--fs-sm);
  color: var(--faint);
  margin-top: var(--sp-3);
  max-width: var(--measure);
}

/* ============================ READOUT =============================== *
 * Cost lens: live operation counters + the step position.
 * ==================================================================== */
#readout {
  display: flex;
  flex-wrap: wrap;
  align-items: baseline;
  justify-content: space-between;
  gap: var(--sp-3);
  margin-top: var(--sp-3);
  padding: var(--sp-3) 0;
  border-top: 1px solid var(--line);
}
.algo-counts {
  display: flex;
  flex-wrap: wrap;
  gap: var(--sp-4);
  font-family: var(--font-mono);
  font-size: var(--fs-sm);
}
.algo-count { display: inline-flex; align-items: baseline; gap: var(--sp-2); }
.algo-count-k { color: var(--muted); }
.algo-count-v {
  color: var(--cost);
  font-variant-numeric: tabular-nums;
  font-weight: 600;
  min-width: 2ch;
  text-align: right;
}
.algo-count-total .algo-count-k { color: var(--faint); }
.algo-count-total .algo-count-v { color: var(--ink); }
.algo-step {
  font-family: var(--font-mono);
  font-size: var(--fs-xs);
  color: var(--faint);
  font-variant-numeric: tabular-nums;
}

/* ========================= CONTROL RAIL ============================= *
 * Declarative widgets (slider/select/toggle/button) + the transport.
 * ==================================================================== */
#controls {
  display: flex;
  flex-wrap: wrap;
  align-items: flex-end;
  gap: var(--sp-4) var(--sp-5);
  padding: var(--sp-4);
  background: var(--panel);
  border: 1px solid var(--line);
  border-radius: var(--radius);
  margin-bottom: var(--sp-5);
}

.algo-field {
  display: flex;
  flex-direction: column;
  gap: var(--sp-2);
  min-width: 140px;
}

.algo-label {
  display: flex;
  align-items: baseline;
  justify-content: space-between;
  gap: var(--sp-2);
  font-family: var(--font-mono);
  font-size: var(--fs-xs);
  text-transform: uppercase;
  letter-spacing: 0.08em;
  color: var(--muted);
}
.algo-value {
  color: var(--accent);
  font-variant-numeric: tabular-nums;
  text-transform: none;
}

/* --- Range inputs (sliders + scrubber + speed): consistent styling --- */
.algo-slider, .algo-scrub, .algo-speed-input {
  -webkit-appearance: none;
  appearance: none;
  width: 100%;
  height: 4px;
  background: var(--line);
  border-radius: 999px;
  cursor: pointer;
}
.algo-slider::-webkit-slider-thumb,
.algo-scrub::-webkit-slider-thumb,
.algo-speed-input::-webkit-slider-thumb {
  -webkit-appearance: none;
  appearance: none;
  width: 16px; height: 16px;
  border-radius: 50%;
  background: var(--accent);
  border: 2px solid var(--bg);
  box-shadow: 0 0 0 1px var(--accent);
}
.algo-slider::-moz-range-thumb,
.algo-scrub::-moz-range-thumb,
.algo-speed-input::-moz-range-thumb {
  width: 14px; height: 14px;
  border-radius: 50%;
  background: var(--accent);
  border: 2px solid var(--bg);
}

/* --- Select --- */
.algo-select {
  font-family: var(--font-mono);
  font-size: var(--fs-sm);
  color: var(--ink);
  background: var(--panel-2);
  border: 1px solid var(--line);
  border-radius: var(--radius-sm);
  padding: var(--sp-2) var(--sp-3);
  cursor: pointer;
}
.algo-select:hover { border-color: var(--muted); }

/* --- Toggle --- */
.algo-toggle {
  display: inline-flex;
  align-items: center;
  gap: var(--sp-2);
  font-family: var(--font-mono);
  font-size: var(--fs-sm);
  color: var(--ink);
  cursor: pointer;
}
.algo-toggle input { width: 16px; height: 16px; accent-color: var(--accent); cursor: pointer; }

/* --- Buttons --- */
.algo-btn {
  font-family: var(--font-mono);
  font-size: var(--fs-sm);
  color: var(--ink);
  background: var(--panel-2);
  border: 1px solid var(--line);
  border-radius: var(--radius-sm);
  padding: var(--sp-2) var(--sp-3);
  cursor: pointer;
  transition: border-color 120ms ease, background 120ms ease;
}
.algo-btn:hover { border-color: var(--accent); background: var(--accent-dim); }
.algo-btn:active { transform: translateY(1px); }
.algo-btn-action { align-self: stretch; }

/* --- Transport bar --- */
.algo-transport {
  display: flex;
  align-items: center;
  gap: var(--sp-3);
  flex: 1 1 320px;
  min-width: 280px;
}
.algo-btn-transport {
  width: 38px; height: 38px;
  display: inline-flex; align-items: center; justify-content: center;
  padding: 0;
  font-size: var(--fs-base);
  line-height: 1;
}
.algo-scrub { flex: 1 1 auto; }
.algo-speed {
  display: flex;
  align-items: center;
  gap: var(--sp-2);
  font-family: var(--font-mono);
  font-size: var(--fs-xs);
  text-transform: uppercase;
  letter-spacing: 0.08em;
  color: var(--muted);
  min-width: 120px;
}
.algo-speed-input { flex: 1 1 auto; }
.algo-railfoot {
  flex-basis: 100%;
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: var(--sp-3) var(--sp-4);
  flex-wrap: wrap;
  margin-top: calc(-1 * var(--sp-1));
}
.algo-keyhint {
  font-family: var(--font-mono);
  font-size: var(--fs-xs);
  color: var(--faint);
  letter-spacing: 0.03em;
}
.algo-copylink {
  flex: 0 0 auto;
  font-family: var(--font-mono);
  font-size: var(--fs-xs);
  color: var(--muted);
  background: transparent;
  border: 1px solid var(--line);
  border-radius: 999px;
  padding: 4px 12px;
  cursor: pointer;
  transition: border-color 140ms ease, color 140ms ease;
}
.algo-copylink:hover { border-color: var(--accent); color: var(--ink); }
.algo-copylink:focus-visible { outline: 2px solid var(--accent); outline-offset: 2px; }
.algo-copylink.copied { color: var(--invariant); border-color: var(--invariant); }

/* ============================== PROSE =============================== *
 * The explainer. One ordered narrative; section headings carry a small
 * monospace eyebrow. References numbered.
 * ==================================================================== */
.prose {
  max-width: var(--measure);
  font-family: var(--font-prose);
  font-size: 1.08rem;
  color: var(--ink);
}
.prose section { margin: var(--sp-8) 0; }
.prose h2 {
  font-family: var(--font-mono);
  font-size: var(--fs-xs);
  font-weight: 600;
  text-transform: uppercase;
  letter-spacing: 0.14em;
  color: var(--accent);
  margin: 0 0 var(--sp-3);
}
.prose h3 {
  font-family: var(--font-prose);
  font-size: var(--fs-lg);
  font-weight: 600;
  margin: var(--sp-5) 0 var(--sp-2);
}
.prose p { margin: 0 0 var(--sp-4); }
.prose strong { color: var(--ink); font-weight: 600; }
.prose em { color: var(--muted); }

/* Inline code + the invariant phrase get a subtle highlight. */
.prose code {
  font-size: 0.92em;
  background: var(--panel-2);
  padding: 0.1em 0.4em;
  border-radius: 4px;
  color: var(--ink);
}
.prose .invariant-term {
  color: var(--invariant);
  font-style: normal;
  font-family: var(--font-mono);
  font-size: 0.92em;
}

/* The rule: pseudocode block — monospace, distinct surface. */
.prose pre, .pseudocode {
  font-family: var(--font-mono);
  font-size: var(--fs-sm);
  line-height: 1.6;
  color: var(--ink);
  background: var(--panel);
  border: 1px solid var(--line);
  border-left: 3px solid var(--accent);
  border-radius: var(--radius-sm);
  padding: var(--sp-4);
  overflow-x: auto;
  white-space: pre;
  tab-size: 2;
}

/* Cost: a small definition grid for time/space best/avg/worst. */
.cost-grid {
  display: grid;
  grid-template-columns: auto repeat(3, 1fr);
  gap: var(--sp-2) var(--sp-4);
  font-family: var(--font-mono);
  font-size: var(--fs-sm);
  margin: var(--sp-4) 0;
}
.cost-grid .cost-head { color: var(--faint); text-transform: uppercase; letter-spacing: 0.08em; font-size: var(--fs-xs); }
.cost-grid .cost-row-label { color: var(--muted); }
.cost-grid .cost-cell { color: var(--cost); font-variant-numeric: tabular-nums; }

/* References: numbered list. */
.prose .references {
  list-style: none;
  counter-reset: ref;
  padding: 0;
  font-family: var(--font-sans);
  font-size: var(--fs-sm);
  color: var(--muted);
}
.prose .references li {
  counter-increment: ref;
  position: relative;
  padding-left: 2.4em;
  margin-bottom: var(--sp-3);
}
.prose .references li::before {
  content: "[" counter(ref) "]";
  position: absolute;
  left: 0;
  font-family: var(--font-mono);
  color: var(--faint);
}

/* "Try this" prompt — invites manipulation (a core principle). */
.prose .try-this {
  background: var(--panel);
  border: 1px solid var(--line);
  border-radius: var(--radius);
  padding: var(--sp-4) var(--sp-5);
}

/* ========================= MAP / HOME PAGE ========================== *
 * Cards in a grid, grouped by family. (The map is generated later by
 * tools/build.mjs; the styles exist now so it lands consistent.)
 * ==================================================================== */
.atlas-head { text-align: center; margin: var(--sp-8) 0 var(--sp-10); }
.atlas-head .kicker {
  font-family: var(--font-mono);
  font-size: var(--fs-xs);
  text-transform: uppercase;
  letter-spacing: 0.2em;
  color: var(--accent);
}
.atlas-head h1 {
  font-family: var(--font-prose);
  font-weight: 600;
  font-size: clamp(2rem, 6vw, 3.4rem);
  margin: var(--sp-3) 0 var(--sp-3);
  letter-spacing: -0.02em;
}
.atlas-head .lede {
  font-family: var(--font-prose);
  font-size: var(--fs-lg);
  color: var(--muted);
  max-width: 60ch;
  margin: 0 auto;
}
.atlas-nav {
  margin-top: var(--sp-4);
  font-family: var(--font-mono);
  font-size: var(--fs-sm);
  color: var(--faint);
  letter-spacing: 0.04em;
}
.prose section h3 {
  font-family: var(--font-prose);
  font-size: var(--fs-lg);
  font-weight: 600;
  margin: var(--sp-5) 0 var(--sp-1);
}

/* Search / filter bar for the map. */
.atlas-toolbar {
  display: flex;
  flex-wrap: wrap;
  gap: var(--sp-3);
  justify-content: center;
  margin-bottom: var(--sp-8);
}
.atlas-search {
  font-family: var(--font-mono);
  font-size: var(--fs-sm);
  color: var(--ink);
  background: var(--panel-2);
  border: 1px solid var(--line);
  border-radius: var(--radius-sm);
  padding: var(--sp-3) var(--sp-4);
  min-width: min(420px, 90vw);
}
.atlas-random {
  font-family: var(--font-mono);
  font-size: var(--fs-sm);
  color: var(--ink);
  background: var(--panel-2);
  border: 1px solid var(--line);
  border-radius: var(--radius-sm);
  padding: var(--sp-3) var(--sp-4);
  cursor: pointer;
  white-space: nowrap;
  transition: border-color 140ms ease, color 140ms ease, transform 140ms ease;
}
.atlas-random:hover { border-color: var(--accent); color: var(--accent); transform: translateY(-1px); }
.atlas-random:active { transform: translateY(0); }
.atlas-random:focus-visible { outline: 2px solid var(--accent); outline-offset: 2px; }
.atlas-empty {
  text-align: center;
  color: var(--muted);
  font-family: var(--font-prose);
  font-size: var(--fs-lg);
  margin: var(--sp-9) auto;
  max-width: 50ch;
}
.atlas-empty[hidden] { display: none; }
.atlas-empty strong { color: var(--ink); }

/* A family group. */
/* Wings — the two halves of the atlas (classic foundations, advanced wing). */
.wing { margin-bottom: var(--sp-10); }
.wing-head { margin: 0 0 var(--sp-6); }
.wing-title {
  font-family: var(--font-prose);
  font-size: var(--fs-xl);
  font-weight: 700;
  letter-spacing: -0.01em;
  margin: 0;
}
.wing-title .wing-count {
  font-family: var(--font-mono);
  font-size: var(--fs-sm);
  font-weight: 400;
  color: var(--faint);
  margin-left: var(--sp-2);
  vertical-align: middle;
}
.wing-blurb {
  font-family: var(--font-prose);
  font-size: var(--fs-base);
  color: var(--muted);
  max-width: 70ch;
  margin: var(--sp-2) 0 0;
}

.family-group { margin-bottom: var(--sp-8); }
.family-group > h3 {
  font-family: var(--font-mono);
  font-size: var(--fs-sm);
  text-transform: uppercase;
  letter-spacing: 0.12em;
  color: var(--muted);
  border-bottom: 1px solid var(--line);
  padding-bottom: var(--sp-2);
  margin: 0 0 var(--sp-4);
  font-weight: 400;
}
.family-group > h3 .count { color: var(--faint); margin-left: var(--sp-2); }

/* The card grid. */
.card-grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(260px, 1fr));
  gap: var(--sp-4);
}
.entry-card {
  display: flex;
  flex-direction: column;
  background: var(--panel);
  border: 1px solid var(--line);
  border-radius: var(--radius);
  overflow: hidden;
  color: inherit;
  text-decoration: none;
  transition: border-color 140ms ease, transform 140ms ease, background 140ms ease, box-shadow 140ms ease;
}
.entry-card:hover {
  border-color: var(--accent);
  background: var(--panel-2);
  transform: translateY(-3px);
  box-shadow: 0 8px 24px rgba(0, 0, 0, 0.35);
  text-decoration: none;
}
.entry-card .card-thumb {
  display: block;
  width: 100%;
  aspect-ratio: 16 / 9;
  object-fit: cover;
  object-position: center;
  background: var(--bg);
  border-bottom: 1px solid var(--line);
}
.entry-card .card-thumb[src=""], .entry-card .card-thumb:not([src]) { display: none; }
.entry-card .card-thumb { transition: filter 140ms ease; }
.entry-card:hover .card-thumb { filter: brightness(1.07) saturate(1.04); }
.entry-card .card-media { position: relative; display: block; }
/* "live demo" play affordance — fades in on hover/focus */
.entry-card .card-play {
  position: absolute; left: 50%; top: 50%;
  transform: translate(-50%, -50%) scale(0.82);
  width: 46px; height: 46px; border-radius: 50%;
  display: grid; place-items: center;
  font-size: 15px; padding-left: 2px;
  color: var(--ink);
  background: rgba(15, 17, 23, 0.72);
  border: 1px solid var(--line);
  opacity: 0; pointer-events: none;
  transition: opacity 150ms ease, transform 150ms ease;
}
.entry-card:hover .card-play,
.entry-card:focus-visible .card-play { opacity: 1; transform: translate(-50%, -50%) scale(1); }
.entry-card:focus-visible {
  outline: 2px solid var(--accent);
  outline-offset: 2px;
  border-color: var(--accent);
}
.entry-card .card-body { padding: var(--sp-4); }
.entry-card .card-cost {
  display: inline-block;
  margin-top: var(--sp-3);
  font-family: var(--font-mono);
  font-size: var(--fs-xs);
  letter-spacing: 0.02em;
  color: var(--cost);
  background: rgba(199, 146, 234, 0.10);
  border: 1px solid rgba(199, 146, 234, 0.22);
  border-radius: 999px;
  padding: 2px 9px;
}
.entry-card .card-family {
  font-family: var(--font-mono);
  font-size: var(--fs-xs);
  text-transform: uppercase;
  letter-spacing: 0.1em;
  color: var(--faint);
}
.entry-card h3 {
  font-family: var(--font-prose);
  font-size: var(--fs-lg);
  font-weight: 600;
  margin: var(--sp-2) 0 var(--sp-1);
}
.entry-card p {
  font-size: var(--fs-sm);
  color: var(--muted);
  margin: 0;
}
.entry-card[data-status="draft"] { opacity: 0.6; }
.entry-card .card-badge {
  font-family: var(--font-mono);
  font-size: var(--fs-xs);
  color: var(--warn);
}

/* Glossary jump-to TOC + deep-linkable terms. */
.glossary-toc {
  display: flex;
  flex-wrap: wrap;
  gap: var(--sp-2) var(--sp-3);
  margin: var(--sp-6) 0 var(--sp-2);
}
.glossary-toc a {
  font-family: var(--font-mono);
  font-size: var(--fs-xs);
  color: var(--accent);
  text-decoration: none;
  border: 1px solid var(--line);
  border-radius: 999px;
  padding: 3px 11px;
  transition: border-color 140ms ease, background 140ms ease;
}
.glossary-toc a:hover { border-color: var(--accent); background: var(--panel); }
.glossary-toc a:focus-visible { outline: 2px solid var(--accent); outline-offset: 2px; }
.prose h3[id] { scroll-margin-top: var(--sp-6); }
.prose h3:target { color: var(--accent); }

/* Graceful degradation: shown only when JavaScript is unavailable. */
.stage-noscript {
  position: absolute;
  inset: 0;
  margin: 0;
  display: flex;
  align-items: center;
  justify-content: center;
  text-align: center;
  padding: var(--sp-7) var(--sp-6);
  color: var(--muted);
  font-family: var(--font-prose);
  font-size: var(--fs-lg);
}

/* "Related" — conceptual cross-links to neighbouring algorithms. */
.related {
  margin-top: var(--sp-9);
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  gap: var(--sp-2) var(--sp-3);
  font-family: var(--font-mono);
  font-size: var(--fs-sm);
}
.related-label {
  text-transform: uppercase;
  letter-spacing: 0.1em;
  font-size: var(--fs-xs);
  color: var(--faint);
}
.related a {
  color: var(--accent);
  text-decoration: none;
  border: 1px solid var(--line);
  border-radius: 999px;
  padding: 3px 12px;
  transition: border-color 140ms ease, background 140ms ease;
}
.related a:hover { border-color: var(--accent); background: var(--panel); text-decoration: none; }
.related a:focus-visible { outline: 2px solid var(--accent); outline-offset: 2px; }

/* Prev / next entry navigation (tour the atlas without returning home). */
.entry-nav {
  display: flex;
  align-items: stretch;
  gap: var(--sp-3);
  margin-top: var(--sp-9);
  padding-top: var(--sp-5);
  border-top: 1px solid var(--line);
  font-family: var(--font-mono);
  font-size: var(--fs-sm);
}
.entry-nav a {
  flex: 1;
  display: flex;
  align-items: center;
  padding: var(--sp-3) var(--sp-4);
  background: var(--panel);
  border: 1px solid var(--line);
  border-radius: var(--radius-sm);
  color: var(--muted);
  text-decoration: none;
  transition: border-color 140ms ease, color 140ms ease, background 140ms ease;
}
.entry-nav a:hover { border-color: var(--accent); color: var(--ink); background: var(--panel-2); text-decoration: none; }
.entry-nav a:focus-visible { outline: 2px solid var(--accent); outline-offset: 2px; }
.entry-nav .nav-next { justify-content: flex-end; text-align: right; }
.entry-nav .nav-home { flex: 0 0 auto; justify-content: center; color: var(--faint); }
.entry-nav .nav-spacer { flex: 1; }
@media (max-width: 560px) {
  .entry-nav { flex-direction: column; }
  .entry-nav .nav-next { justify-content: flex-start; text-align: left; }
}

/* ============================== FOOTER ============================== */
.site-footer {
  margin-top: var(--sp-10);
  padding-top: var(--sp-5);
  border-top: 1px solid var(--line);
  font-size: var(--fs-sm);
  color: var(--faint);
  text-align: center;
}

/* ============================ RESPONSIVE ============================ */
@media (max-width: 640px) {
  .page { padding: var(--sp-4) var(--sp-4) var(--sp-8); }
  .entry-head h1 { font-size: var(--fs-xl); }
  #controls { gap: var(--sp-4); }
  .algo-field { min-width: 100%; }
  .algo-transport { flex-basis: 100%; }
  #stage { height: clamp(220px, 60vw, 360px); }
  .cost-grid { grid-template-columns: 1fr; }
  .cost-grid .cost-head { display: none; }
}

/* --------------------- Reduced motion / a11y ------------------------ */
@media (prefers-reduced-motion: reduce) {
  * {
    animation-duration: 0.001ms !important;
    animation-iteration-count: 1 !important;
    transition-duration: 0.001ms !important;
    scroll-behavior: auto !important;
  }
  .entry-card:hover { transform: none; }
}