:root {
  color-scheme: light dark;

  --canvas: #f5f4f0;
  --paper: #fbfaf7;
  --ink: #20201d;
  --muted: #6b6961;
  --line: #d7d4cc;
  --line-strong: #aaa69d;
  --accent: #355f73;
  --accent-hover: #274b5c;
  --accent-soft: #e5eef1;
  --code: #efeee9;

  --space-1: .25rem;
  --space-2: .5rem;
  --space-3: .75rem;
  --space-4: 1rem;
  --space-5: 1.5rem;
  --space-6: 2rem;
  --space-7: 3rem;
  --space-8: 4.5rem;
  --space-9: 6rem;

  --page-max: 73.75rem;
  --reading-max: 46rem;
  --wide-copy: 54rem;
  --radius: 3px;

  font-family:
    system-ui,
    -apple-system,
    BlinkMacSystemFont,
    "Hiragino Sans",
    "Yu Gothic UI",
    "Yu Gothic",
    Meiryo,
    "Segoe UI",
    sans-serif;
}

* { box-sizing: border-box; }

html {
  background: var(--canvas);
  color: var(--ink);
  -webkit-text-size-adjust: 100%;
  text-size-adjust: 100%;
  scroll-behavior: smooth;
}

body {
  margin: 0;
  min-width: 320px;
  background: var(--canvas);
  color: var(--ink);
  font-size: 1rem;
  line-height: 1.76;
  text-rendering: optimizeLegibility;
}

::selection { background: var(--accent-soft); color: var(--ink); }

a {
  color: var(--accent);
  text-decoration-thickness: .08em;
  text-underline-offset: .18em;
}
a:hover { color: var(--accent-hover); }
a:focus-visible,
button:focus-visible,
summary:focus-visible {
  outline: 2px solid var(--accent);
  outline-offset: 3px;
}

p, h1, h2, h3, dl, dd, ul, ol { margin-top: 0; }
h1, h2, h3, strong { font-weight: 700; }
h1, h2, h3 {
  color: var(--ink);
  text-wrap: pretty;
  overflow-wrap: normal;
  word-break: normal;
}
code, pre { font-family: ui-monospace, SFMono-Regular, Menlo, Consolas, monospace; }
code { overflow-wrap: anywhere; }

.skip-link {
  position: fixed;
  z-index: 100;
  top: var(--space-3);
  left: var(--space-3);
  padding: .6rem .8rem;
  background: var(--ink);
  color: var(--canvas);
  border-radius: var(--radius);
  transform: translateY(-180%);
  transition: transform 120ms ease;
}
.skip-link:focus { transform: translateY(0); }

.site-header { border-bottom: 1px solid var(--line); }
.site-header-inner,
.site-footer-inner,
main {
  width: min(var(--page-max), calc(100% - 3rem));
  margin-inline: auto;
}
.site-header-inner {
  min-height: 4.5rem;
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: var(--space-5);
}
.site-brand {
  min-height: 44px;
  display: inline-flex;
  align-items: baseline;
  gap: var(--space-3);
  color: var(--ink);
  text-decoration: none;
  white-space: nowrap;
}
.site-brand:hover { color: var(--ink); }
.site-brand-name { font-size: .98rem; font-weight: 800; letter-spacing: -.02em; }
.site-brand-meta { color: var(--muted); font-size: .7rem; font-weight: 650; letter-spacing: .025em; }
.site-nav { display: flex; align-items: center; justify-content: flex-end; gap: var(--space-2); }
.site-nav a {
  min-height: 44px;
  display: inline-flex;
  align-items: center;
  padding-inline: .7rem;
  color: var(--muted);
  font-size: .86rem;
  font-weight: 650;
  text-decoration: none;
}
.site-nav a:hover,
.site-nav a[aria-current="page"] {
  color: var(--ink);
  text-decoration: underline;
  text-underline-offset: .2em;
}

main { padding-block: var(--space-8) var(--space-9); }
.hero { max-width: 64rem; padding-block: var(--space-4) var(--space-8); }
.hero-compact { max-width: 58rem; padding-bottom: var(--space-7); }
.eyebrow,
.section-kicker,
.route-label,
.hypothesis-label {
  margin-bottom: var(--space-3);
  color: var(--muted);
  font-size: .75rem;
  font-weight: 750;
  letter-spacing: .035em;
}
.hero h1 {
  max-width: 16ch;
  margin-bottom: var(--space-5);
  font-size: clamp(2.55rem, 6.2vw, 5rem);
  line-height: 1.04;
  letter-spacing: -.055em;
}
.hero-compact h1 { max-width: 14ch; font-size: clamp(2.35rem, 5vw, 4.25rem); }
.lead {
  max-width: var(--wide-copy);
  margin-bottom: 0;
  color: var(--muted);
  font-size: clamp(1.05rem, 1.55vw, 1.22rem);
  line-height: 1.78;
}
.lead strong { color: var(--ink); }

.actions { display: flex; flex-wrap: wrap; align-items: center; gap: var(--space-3); margin-top: var(--space-6); }
.hero-actions { margin-top: var(--space-6); }
.button {
  min-height: 44px;
  display: inline-flex;
  align-items: center;
  justify-content: center;
  padding: .68rem .95rem;
  border: 1px solid var(--line-strong);
  border-radius: var(--radius);
  background: transparent;
  color: var(--ink);
  font-size: .9rem;
  font-weight: 700;
  line-height: 1.2;
  text-decoration: none;
}
.button:hover { border-color: var(--ink); color: var(--ink); }
.button.primary { border-color: var(--accent); background: var(--accent); color: #fff; }
.button.primary:hover { border-color: var(--accent-hover); background: var(--accent-hover); color: #fff; }

.boundary-line {
  list-style: none;
  display: flex;
  flex-wrap: wrap;
  gap: .2rem 1.25rem;
  padding: var(--space-5) 0 0;
  margin: var(--space-6) 0 0;
  border-top: 1px solid var(--line);
  color: var(--muted);
  font-size: .78rem;
}
.boundary-line li { position: relative; padding-left: .9rem; }
.boundary-line li::before { content: "—"; position: absolute; left: 0; color: var(--line-strong); }

.content-section {
  display: grid;
  grid-template-columns: minmax(11rem, .28fr) minmax(0, 1fr);
  gap: var(--space-7);
  padding-block: var(--space-8);
  border-top: 1px solid var(--line);
}
.section-heading { min-width: 0; }
.section-heading h2 {
  margin-bottom: var(--space-4);
  font-size: clamp(1.55rem, 3vw, 2.25rem);
  line-height: 1.18;
  letter-spacing: -.04em;
}
.section-heading > p:last-child {
  max-width: 31rem;
  margin-bottom: 0;
  color: var(--muted);
  font-size: .93rem;
  line-height: 1.72;
}
.content-section > :not(.section-heading) { min-width: 0; }

.relation-list,
.option-list,
.rule-list,
.compact-ordered-list { list-style: none; padding: 0; margin: 0; }
.relation-list { border-top: 1px solid var(--line); }
.relation-list li {
  display: grid;
  grid-template-columns: minmax(8.5rem, .32fr) 2.5rem minmax(0, 1fr);
  gap: var(--space-4);
  align-items: start;
  padding: 1.05rem 0;
  border-bottom: 1px solid var(--line);
}
.relation-list > li > strong,
.relation-list > li > span > strong { font-size: .98rem; }
.relation-list small {
  display: block;
  max-width: 36rem;
  margin-top: .2rem;
  color: var(--muted);
  font-size: .8rem;
  line-height: 1.55;
}
.relation-symbol { color: var(--line-strong); font-size: 1.08rem; font-weight: 650; text-align: center; }

.note {
  grid-column: 2;
  max-width: var(--reading-max);
  margin: var(--space-5) 0 0;
  padding-left: var(--space-4);
  border-left: 2px solid var(--line-strong);
  color: var(--muted);
  font-size: .88rem;
  line-height: 1.7;
}

.flow {
  list-style: none;
  padding: 0;
  margin: 0;
  counter-reset: step;
  border-top: 1px solid var(--line);
}
.flow li {
  counter-increment: step;
  display: grid;
  grid-template-columns: 2.2rem minmax(0, 1fr);
  gap: var(--space-4);
  padding: 1.1rem 0;
  border-bottom: 1px solid var(--line);
}
.flow li::before {
  content: "0" counter(step);
  color: var(--muted);
  font-size: .7rem;
  font-variant-numeric: tabular-nums;
  font-weight: 700;
  letter-spacing: .02em;
  padding-top: .12rem;
}
.flow li > div { max-width: var(--reading-max); }
.flow strong { color: var(--ink); }

.hypothesis-example {
  border: 1px solid var(--line-strong);
  border-radius: var(--radius);
  background: var(--paper);
}
.hypothesis-header { padding: var(--space-6); border-bottom: 1px solid var(--line); }
.hypothesis-header h3 {
  max-width: 44rem;
  margin: 0;
  font-size: clamp(1.15rem, 2vw, 1.45rem);
  line-height: 1.55;
  letter-spacing: -.02em;
}
.hypothesis-label { margin-bottom: var(--space-2); }
.hypothesis-details { margin: 0; }
.hypothesis-details > div {
  display: grid;
  grid-template-columns: minmax(8.5rem, .28fr) minmax(0, 1fr);
  gap: var(--space-5);
  padding: .95rem var(--space-6);
  border-bottom: 1px solid var(--line);
}
.hypothesis-details dt { color: var(--muted); font-size: .76rem; font-weight: 750; }
.hypothesis-details dd {
  margin: 0;
  max-width: 40rem;
  font-size: .91rem;
  line-height: 1.65;
  overflow-wrap: anywhere;
}
.hypothesis-example details { border: 0; }
.hypothesis-example summary {
  min-height: 48px;
  display: flex;
  align-items: center;
  padding: .75rem var(--space-6);
  color: var(--muted);
  cursor: pointer;
  font-size: .82rem;
  font-weight: 700;
}
.hypothesis-example details p {
  max-width: var(--reading-max);
  margin: 0;
  padding: 0 var(--space-6) var(--space-6);
  color: var(--muted);
  font-size: .88rem;
}
.content-section > p:not(.note) {
  grid-column: 2;
  max-width: var(--reading-max);
  margin-bottom: 0;
  color: var(--muted);
  font-size: .9rem;
}

.option-list {
  display: grid;
  grid-template-columns: repeat(2, minmax(0, 1fr));
  border-top: 1px solid var(--line);
}
.option-list li {
  display: grid;
  gap: .2rem;
  min-height: 6rem;
  align-content: start;
  padding: 1rem 0;
  border-bottom: 1px solid var(--line);
}
.option-list li:nth-child(odd) { padding-right: var(--space-5); }
.option-list li:nth-child(even) { padding-left: var(--space-5); border-left: 1px solid var(--line); }
.option-list span { color: var(--muted); font-size: .84rem; line-height: 1.58; }

.route-list { border-top: 1px solid var(--line); }
.route-row {
  display: grid;
  grid-template-columns: minmax(12rem, .38fr) minmax(0, 1fr);
  gap: var(--space-6);
  padding: 1.2rem 0;
  border-bottom: 1px solid var(--line);
}
.route-row h3 { margin: 0; font-size: 1.05rem; line-height: 1.45; }
.route-row p:last-child {
  max-width: 36rem;
  margin: 0;
  color: var(--muted);
  font-size: .88rem;
  overflow-wrap: anywhere;
}
.route-label { margin-bottom: .15rem; }

.boundary-map,
.mini-definition-list { margin: 0; }
.boundary-map { border-top: 1px solid var(--line); }
.boundary-map > div {
  display: grid;
  grid-template-columns: minmax(10rem, .3fr) minmax(0, 1fr);
  gap: var(--space-5);
  padding: 1rem 0;
  border-bottom: 1px solid var(--line);
}
.boundary-map dt,
.mini-definition-list dt { color: var(--muted); font-size: .76rem; font-weight: 750; }
.boundary-map dd,
.mini-definition-list dd {
  margin: 0;
  font-size: .9rem;
  line-height: 1.62;
  overflow-wrap: anywhere;
}

.reference-actions { grid-column: 2; }
.deep-reference { padding-bottom: var(--space-7); }
.reference-list { border-top: 1px solid var(--line); }
.reference-list a {
  min-height: 52px;
  display: grid;
  grid-template-columns: minmax(0, 1fr) 1.5rem;
  gap: var(--space-4);
  align-items: center;
  padding: .8rem 0;
  border-bottom: 1px solid var(--line);
  color: var(--ink);
  font-size: .9rem;
  font-weight: 650;
  text-decoration: none;
  overflow-wrap: anywhere;
}
.reference-list a span:last-child { color: var(--muted); text-align: right; }
.reference-list a:hover span:first-child { text-decoration: underline; text-underline-offset: .18em; }

.rule-list { border-top: 1px solid var(--line); }
.rule-list li {
  position: relative;
  padding: .85rem 0 .85rem 1.25rem;
  border-bottom: 1px solid var(--line);
  font-size: .9rem;
  overflow-wrap: anywhere;
}
.rule-list li::before { content: "—"; position: absolute; left: 0; color: var(--line-strong); }
.two-column-rules { display: grid; grid-template-columns: repeat(2, minmax(0, 1fr)); }
.two-column-rules li:nth-child(odd) { padding-right: var(--space-5); }
.two-column-rules li:nth-child(even) {
  padding-left: calc(var(--space-5) + 1.25rem);
  border-left: 1px solid var(--line);
}
.two-column-rules li:nth-child(even)::before { left: var(--space-5); }

.retrieval-groups {
  display: grid;
  grid-template-columns: minmax(0, 1.25fr) minmax(0, .75fr);
  gap: var(--space-7);
}
.retrieval-groups h3 { margin-bottom: var(--space-3); font-size: .9rem; }
.compact-ordered-list { counter-reset: retrieval; border-top: 1px solid var(--line); }
.compact-ordered-list li {
  counter-increment: retrieval;
  display: grid;
  grid-template-columns: 2rem minmax(0, 1fr);
  min-height: 44px;
  align-items: center;
  border-bottom: 1px solid var(--line);
  font-size: .86rem;
}
.compact-ordered-list li::before {
  content: counter(retrieval, decimal-leading-zero);
  color: var(--muted);
  font-size: .68rem;
  font-variant-numeric: tabular-nums;
}
.mini-definition-list { border-top: 1px solid var(--line); }
.mini-definition-list > div { padding: .8rem 0; border-bottom: 1px solid var(--line); }
.mini-definition-list dd { margin-top: .2rem; }

.site-footer { border-top: 1px solid var(--line); }
.site-footer-inner {
  display: grid;
  grid-template-columns: minmax(14rem, .42fr) minmax(0, 1fr);
  gap: var(--space-8);
  padding-block: var(--space-7) var(--space-8);
}
.footer-statement { display: grid; align-content: start; gap: var(--space-2); }
.footer-statement strong { font-size: 1rem; }
.footer-statement span {
  max-width: 27rem;
  color: var(--muted);
  font-size: .75rem;
  line-height: 1.6;
}
.footer-links { display: grid; grid-template-columns: repeat(2, minmax(0, 1fr)); gap: var(--space-6); }
.footer-links nav { display: grid; align-content: start; }
.footer-links p {
  margin-bottom: var(--space-2);
  color: var(--muted);
  font-size: .7rem;
  font-weight: 750;
  letter-spacing: .035em;
}
.footer-links a {
  min-height: 44px;
  display: inline-flex;
  align-items: center;
  width: fit-content;
  max-width: 100%;
  color: var(--muted);
  font-size: .82rem;
  overflow-wrap: anywhere;
}
.footer-links a:hover { color: var(--ink); }

pre {
  max-width: 100%;
  overflow-x: auto;
  padding: var(--space-5);
  border: 1px solid var(--line);
  border-radius: var(--radius);
  background: var(--code);
  color: var(--ink);
  font-size: .82rem;
  line-height: 1.65;
  white-space: pre;
}

@media (prefers-color-scheme: dark) {
  :root {
    --canvas: #181918;
    --paper: #1e1f1d;
    --ink: #f0efe9;
    --muted: #aaa89f;
    --line: #393a35;
    --line-strong: #5a5b54;
    --accent: #96bfd0;
    --accent-hover: #b1d3df;
    --accent-soft: #24343b;
    --code: #252622;
  }
  .button.primary { color: #10232b; }
  .button.primary:hover { color: #0d1c22; }
}

@media (max-width: 860px) {
  .site-header-inner { align-items: flex-start; padding-block: .75rem; }
  .site-nav { flex-wrap: wrap; }
  .content-section { grid-template-columns: 1fr; gap: var(--space-5); }
  .content-section > p:not(.note),
  .note,
  .reference-actions { grid-column: 1; }
  .section-heading > p:last-child { max-width: var(--reading-max); }
  .site-footer-inner { grid-template-columns: 1fr; gap: var(--space-6); }
}

@media (max-width: 640px) {
  .site-header-inner,
  .site-footer-inner,
  main { width: min(100% - 1.5rem, var(--page-max)); }

  .site-header-inner {
    display: grid;
    grid-template-columns: 1fr;
    gap: .2rem;
  }
  .site-brand { min-height: 44px; }
  .site-nav {
    justify-content: flex-start;
    gap: 0;
    margin-inline: -.55rem;
  }
  .site-nav a { padding-inline: .55rem; font-size: .82rem; }

  main { padding-block: var(--space-7) var(--space-8); }
  .hero { padding-block: 0 var(--space-7); }
  .hero h1,
  .hero-compact h1 {
    max-width: none;
    font-size: clamp(2.35rem, 11vw, 3.5rem);
    line-height: 1.05;
  }
  .hero h1 br { display: none; }
  .lead { font-size: 1rem; line-height: 1.76; }
  .boundary-line { display: grid; gap: .35rem; }
  .content-section { padding-block: var(--space-7); }

  .relation-list li {
    grid-template-columns: minmax(0, 1fr) 2rem minmax(0, 1.45fr);
    gap: .6rem;
  }
  .relation-list small { font-size: .76rem; }

  .hypothesis-header { padding: var(--space-5); }
  .hypothesis-details > div {
    grid-template-columns: 1fr;
    gap: .2rem;
    padding: .85rem var(--space-5);
  }
  .hypothesis-example summary { padding-inline: var(--space-5); }
  .hypothesis-example details p { padding-inline: var(--space-5); }

  .option-list,
  .two-column-rules,
  .retrieval-groups,
  .footer-links { grid-template-columns: 1fr; }
  .option-list li:nth-child(odd),
  .option-list li:nth-child(even),
  .two-column-rules li:nth-child(odd),
  .two-column-rules li:nth-child(even) {
    padding-left: 0;
    padding-right: 0;
    border-left: 0;
  }
  .two-column-rules li:nth-child(even) { padding-left: 1.25rem; }
  .two-column-rules li:nth-child(even)::before { left: 0; }

  .route-row,
  .boundary-map > div { grid-template-columns: 1fr; gap: .35rem; }
  .actions { align-items: stretch; }
  .button { text-align: center; }
  .reference-actions .button { flex: 1 1 100%; }
  .site-footer-inner { padding-block: var(--space-6) var(--space-7); }
}

@media (max-width: 480px) {
  .relation-list li {
    grid-template-columns: minmax(0, 1fr) 1.5rem;
    gap: .35rem .55rem;
  }
  .relation-list li > span:last-child {
    grid-column: 1 / -1;
    padding-left: 1rem;
  }
  .relation-list small { max-width: none; }

  .actions .button { flex: 1 1 100%; }
  .reference-list a { min-height: 56px; }
}

@media (max-width: 390px) {
  .site-header-inner,
  .site-footer-inner,
  main { width: calc(100% - 1.25rem); }
  .site-brand-meta { display: none; }
  .site-nav a {
    min-height: 44px;
    font-size: .79rem;
    padding-inline: .48rem;
  }
}

@media (prefers-reduced-motion: reduce) {
  html { scroll-behavior: auto; }
  .skip-link { transition: none; }
}

@media (forced-colors: active) {
  a:focus-visible,
  button:focus-visible,
  summary:focus-visible {
    outline: 2px solid CanvasText;
  }
  .button,
  .hypothesis-example {
    border-color: CanvasText;
  }
  .relation-symbol,
  .boundary-line li::before,
  .rule-list li::before {
    color: CanvasText;
  }
}