:root {
  --color-surface: #f5f4f4;
  --color-surface-alt: #edebeb;
  --color-surface-deep: #e1dfdf;
  --color-ink: #524243;
  --color-ink-soft: #7c6567;
  --color-ink-muted: #8b7476;
  --color-line: #d8d4d4;
  --color-primary: #dd2231;
  --color-primary-ink: #ffffff;
  --color-primary-soft: #f2d7d9;
  --color-accent: #a6690c;
  --color-accent-ink: #ffffff;
  --color-highlight: #e7dbca;
  --color-focus: #9b5e03;
  --color-contrast-surface: #2b1618;
  --color-contrast-ink: #e7e4e4;
  --color-contrast-line: #544345;
  --color-contrast-accent: #ed9512;
  --overlay-scrim: linear-gradient(180deg, rgba(43, 22, 24, 0.35) 0%, rgba(43, 22, 24, 0.72) 55%, rgba(43, 22, 24, 0.92) 100%);
  --font-heading: "Songti SC", STSong, "Source Han Serif SC", SimSun, serif;
  --font-body: "Songti SC", STSong, "Source Han Serif SC", SimSun, serif;
  --font-mono: ui-monospace, Menlo, Consolas, monospace;
  --text-xs: 12.2px;
  --text-sm: 15.2px;
  --text-base: 17px;
  --text-lg: 21.2px;
  --text-xl: 26.6px;
  --text-2xl: 33.2px;
  --text-3xl: 41.5px;
  --text-4xl: 51.9px;
  --text-display: clamp(34px, 5.7vw, 73px);
  --text-figure: clamp(28px, 4.1vw, 53px);
  --weight-heading: 672;
  --weight-body: 400;
  --leading-body: 1.85;
  --leading-heading: 1.16;
  --tracking-heading: 0.04em;
  --radius-sm: 1px;
  --radius-md: 1px;
  --radius-lg: 1px;
  --radius-pill: 1px;
  --border-thin: 1px;
  --border-thick: 2px;
  --shadow-1: none;
  --shadow-2: none;
  --space-1: 8px;
  --space-2: 16px;
  --space-3: 24px;
  --space-4: 32px;
  --space-6: 48px;
  --space-8: 64px;
  --container: 1080px;
  --measure: 68ch;
  --gutter: 32px;
  --section-y: 105px;
  --section-y-lg: 147px;
}

/* ========== reset ========== */
*, *::before, *::after { box-sizing: border-box; }
html { -webkit-text-size-adjust: 100%; }
@media (prefers-reduced-motion: no-preference) { html { scroll-behavior: smooth; } }
body, h1, h2, h3, h4, h5, p, ul, ol, dl, dd, figure, blockquote, table { margin: 0; }
ul, ol { padding: 0; list-style: none; }
img, svg, video { display: block; max-width: 100%; }
a { color: inherit; text-decoration: none; }
button { font: inherit; color: inherit; background: none; border: 0; cursor: pointer; }
table { border-collapse: collapse; }
:focus-visible { outline: var(--border-thick) solid var(--color-focus); outline-offset: 3px; }

/* ========== base ========== */
body {
  background-color: var(--color-surface);
  color: var(--color-ink);
  font-family: var(--font-body);
  font-size: var(--text-base);
  font-weight: var(--weight-body);
  line-height: var(--leading-body);
  letter-spacing: 0.01em;
}
h1, h2, h3, h4 {
  font-family: var(--font-heading);
  font-weight: var(--weight-heading);
  line-height: var(--leading-heading);
  letter-spacing: var(--tracking-heading);
}
h1 { font-size: var(--text-3xl); }
h2 { font-size: var(--text-2xl); }
h3 { font-size: var(--text-xl); }
h4 { font-size: var(--text-lg); }
p { max-width: var(--measure); }

.container {
  width: 100%;
  max-width: var(--container);
  margin-inline: auto;
  padding-inline: var(--space-3);
}

/* ========== section rhythm ========== */
.section { padding-block: var(--section-y); }
.section--lg { padding-block: var(--section-y-lg); }
.section--sm { padding-block: var(--space-6); }
.section--alt { background-color: var(--color-surface-alt); }
.section--deep { background-color: var(--color-surface-deep); }
.section--contrast {
  background-color: var(--color-contrast-surface);
  color: var(--color-contrast-ink);
  border-block: 3px double var(--color-contrast-line);
}
.section--contrast h1, .section--contrast h2, .section--contrast h3, .section--contrast h4 { color: var(--color-contrast-ink); }
.section--contrast .section-head__title { color: var(--color-contrast-ink); }
.section--contrast .section-head__note { color: color-mix(in srgb, var(--color-contrast-ink) 74%, transparent); }

/* ========== headings ========== */
.kicker {
  font-family: var(--font-mono);
  font-size: var(--text-xs);
  letter-spacing: 0.28em;
  color: var(--color-primary);
  text-transform: uppercase;
}
.display {
  font-family: var(--font-heading);
  font-weight: var(--weight-heading);
  font-size: var(--text-display);
  line-height: 1.02;
  letter-spacing: 0.02em;
}
.display em { font-style: normal; color: var(--color-primary); }
.lede {
  font-size: var(--text-lg);
  line-height: 1.7;
  color: var(--color-ink-soft);
  max-width: var(--measure);
}
.meta-line {
  font-family: var(--font-mono);
  font-size: var(--text-xs);
  letter-spacing: 0.1em;
  color: var(--color-ink-muted);
}

.section-head {
  display: grid;
  grid-template-columns: auto minmax(0, 1fr);
  gap: var(--space-2) var(--space-3);
  align-items: start;
  margin-bottom: var(--space-6);
}
.section-head__index {
  grid-row: span 3;
  padding-top: 8px;
  font-family: var(--font-mono);
  font-size: var(--text-sm);
  letter-spacing: 0.12em;
  color: var(--color-primary);
}
.section-head__title { font-size: var(--text-3xl); }
.section-head__note {
  grid-column: 2;
  max-width: var(--measure);
  font-size: var(--text-sm);
  color: var(--color-ink-soft);
}
.section-head__actions { grid-column: 2; display: flex; flex-wrap: wrap; gap: var(--space-2); }
.section-head--center { grid-template-columns: minmax(0, 1fr); justify-items: center; text-align: center; }
.section-head--center .section-head__index { grid-row: auto; padding-top: 0; }
.section-head--center .section-head__note, .section-head--center .section-head__actions { grid-column: 1; justify-content: center; }
.section-head--split {
  grid-template-columns: auto minmax(0, 1fr) auto;
  align-items: end;
  border-bottom: 3px double var(--color-line);
  padding-bottom: var(--space-3);
}
.section-head--split .section-head__index { grid-row: auto; padding-top: 0; }
.section-head--split .section-head__note { grid-column: 2; }
.section-head--split .section-head__actions { grid-column: 3; grid-row: 1 / -1; align-self: end; }

/* ========== dividers ========== */
.rule-double { border: 0; height: 4px; background-image: linear-gradient(180deg, var(--color-line) 0 1px, transparent 1px 3px, var(--color-line) 3px 4px); }
.rule-double--contrast { background-image: linear-gradient(180deg, var(--color-contrast-line) 0 1px, transparent 1px 3px, var(--color-contrast-line) 3px 4px); }
.scale-rule {
  height: 18px;
  border-top: var(--border-thin) solid var(--color-line);
  background-image:
    repeating-linear-gradient(90deg, var(--color-line) 0 1px, transparent 1px 40px),
    repeating-linear-gradient(90deg, var(--color-primary) 0 1px, transparent 1px 200px);
  background-repeat: repeat-x;
  background-size: 40px 6px, 200px 15px;
  background-position: 0 0, 0 0;
}
.divider-dotted { border: 0; border-top: var(--border-thin) dashed var(--color-line); }

/* ========== prose ========== */
.prose { max-width: var(--measure); }
.prose > * + * { margin-top: var(--space-3); }
.prose h2 { font-size: var(--text-2xl); margin-top: var(--space-6); }
.prose h3 { font-size: var(--text-xl); margin-top: var(--space-4); }
.prose ul { display: grid; gap: var(--space-1); }
.prose ul li { position: relative; padding-left: 20px; }
.prose ul li::before {
  content: "";
  position: absolute;
  left: 0;
  top: 0.85em;
  width: 11px;
  border-top: var(--border-thick) solid var(--color-primary);
}
.prose blockquote {
  border-left: var(--border-thick) solid var(--color-primary);
  padding-left: var(--space-3);
  color: var(--color-ink-soft);
}

/* ========== panel ========== */
.panel {
  border: 3px double var(--color-line);
  background-color: var(--color-surface);
  padding: var(--space-4);
}
.panel--alt { background-color: var(--color-surface-alt); }
.panel--deep { background-color: var(--color-surface-deep); }
.panel--contrast { background-color: var(--color-contrast-surface); color: var(--color-contrast-ink); border-color: var(--color-contrast-line); }
.panel__title { font-size: var(--text-lg); margin-bottom: var(--space-2); }

/* ========== buttons ========== */
.btn {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  gap: var(--space-1);
  min-height: 44px;
  padding: 10px var(--space-3);
  border: var(--border-thin) solid var(--color-line);
  border-radius: var(--radius-sm);
  background-color: var(--color-surface);
  color: var(--color-ink);
  font-family: var(--font-heading);
  font-size: var(--text-sm);
  letter-spacing: 0.14em;
  transition: background-color 0.22s ease, color 0.22s ease, border-color 0.22s ease;
}
.btn:hover { border-color: var(--color-primary); color: var(--color-primary); }
.btn--primary {
  background-color: var(--color-primary);
  border-color: var(--color-primary);
  color: var(--color-primary-ink);
}
.btn--primary:hover {
  background-color: color-mix(in srgb, var(--color-primary) 84%, #000);
  border-color: color-mix(in srgb, var(--color-primary) 84%, #000);
  color: var(--color-primary-ink);
}
.btn--outline { background-color: transparent; border: 3px double var(--color-line); }
.btn--outline:hover { border-color: var(--color-primary); }
.btn--accent {
  background-color: var(--color-accent);
  border-color: var(--color-accent);
  color: var(--color-accent-ink);
}
.btn--accent:hover {
  background-color: color-mix(in srgb, var(--color-accent) 86%, #000);
  border-color: color-mix(in srgb, var(--color-accent) 86%, #000);
  color: var(--color-accent-ink);
}
.btn--on-contrast {
  background-color: transparent;
  border-color: var(--color-contrast-line);
  color: var(--color-contrast-ink);
}
.btn--on-contrast:hover { border-color: var(--color-contrast-accent); color: var(--color-contrast-accent); }
.btn--block { width: 100%; }

/* ========== tags ========== */
.tag-row { display: flex; flex-wrap: wrap; gap: var(--space-1); }
.tag {
  display: inline-flex;
  align-items: center;
  gap: 6px;
  padding: 3px 10px;
  border: var(--border-thin) solid var(--color-line);
  border-radius: var(--radius-sm);
  background-color: var(--color-surface);
  color: var(--color-ink-soft);
  font-family: var(--font-mono);
  font-size: var(--text-xs);
  letter-spacing: 0.12em;
  line-height: 1.6;
}
.tag--primary { border-color: var(--color-primary); background-color: var(--color-primary-soft); color: var(--color-primary); }
.tag--accent { border-color: var(--color-accent); background-color: var(--color-highlight); color: var(--color-accent); }
.tag--solid { border-color: var(--color-accent); background-color: var(--color-accent); color: var(--color-accent-ink); }
.tag--contrast {
  border-color: var(--color-contrast-line);
  background-color: transparent;
  color: var(--color-contrast-accent);
}

/* ========== figures & data ========== */
.figure { display: flex; align-items: baseline; gap: 6px; flex-wrap: wrap; }
.figure__value {
  font-family: var(--font-mono);
  font-size: var(--text-figure);
  line-height: 1;
  letter-spacing: -0.01em;
  color: var(--color-accent);
}
.figure__unit { font-family: var(--font-mono); font-size: var(--text-sm); color: var(--color-ink-muted); }
.figure__label { font-size: var(--text-sm); color: var(--color-ink-soft); }
.figure--on-contrast .figure__value { color: var(--color-contrast-accent); }
.figure--on-contrast .figure__unit { color: color-mix(in srgb, var(--color-contrast-ink) 72%, transparent); }
.figure--on-contrast .figure__label { color: var(--color-contrast-ink); }

.stat-strip {
  background-color: var(--color-contrast-surface);
  color: var(--color-contrast-ink);
  border-block: 3px double var(--color-contrast-line);
  padding-block: var(--space-6);
}
.stat-strip__grid { display: grid; grid-template-columns: repeat(4, minmax(0, 1fr)); }
.stat-strip__cell {
  padding: var(--space-2) var(--space-3);
  border-left: var(--border-thin) solid var(--color-contrast-line);
}
.stat-strip__cell:first-child { border-left: 0; padding-left: 0; }
.stat-strip__cell p { max-width: none; }

/* ========== spec table ========== */
.table-scroll { overflow-x: auto; }
.table-scroll::-webkit-scrollbar { height: 8px; }
.table-scroll::-webkit-scrollbar-thumb { background-color: var(--color-line); }
.spec-table {
  width: 100%;
  min-width: 640px;
  border: 3px double var(--color-line);
  background-color: var(--color-surface);
  font-size: var(--text-sm);
}
.spec-table caption {
  caption-side: top;
  text-align: left;
  padding-bottom: var(--space-1);
  font-family: var(--font-mono);
  font-size: var(--text-xs);
  letter-spacing: 0.12em;
  color: var(--color-ink-muted);
}
.spec-table th, .spec-table td {
  padding: 12px var(--space-2);
  border-bottom: var(--border-thin) solid var(--color-line);
  text-align: left;
  vertical-align: top;
  line-height: 1.6;
}
.spec-table thead th {
  background-color: var(--color-surface-deep);
  font-family: var(--font-heading);
  font-size: var(--text-sm);
  letter-spacing: 0.1em;
  color: var(--color-ink);
  white-space: nowrap;
}
.spec-table tbody tr:nth-child(even) { background-color: var(--color-surface-alt); }
.spec-table tbody tr { cursor: pointer; transition: background-color 0.2s ease; }
.spec-table tbody tr:hover { background-color: var(--color-primary-soft); }
.spec-table tbody tr.is-active { background-color: var(--color-highlight); }
.spec-table .num {
  font-family: var(--font-mono);
  text-align: right;
  color: var(--color-accent);
  white-space: nowrap;
}
.spec-table .num small { font-size: var(--text-xs); margin-left: 3px; color: var(--color-ink-muted); }
.spec-table--on-contrast { border-color: var(--color-contrast-line); background-color: transparent; color: var(--color-contrast-ink); }
.spec-table--on-contrast th, .spec-table--on-contrast td { border-bottom-color: var(--color-contrast-line); }
.spec-table--on-contrast thead th { background-color: var(--color-contrast-line); color: var(--color-contrast-ink); }
.spec-table--on-contrast tbody tr:nth-child(even) { background-color: color-mix(in srgb, var(--color-contrast-ink) 6%, transparent); }
.spec-table--on-contrast .num { color: var(--color-contrast-accent); }

/* ========== media blocks ========== */
.media {
  position: relative;
  overflow: hidden;
  aspect-ratio: 16 / 9;
  background-color: var(--color-surface-deep);
  border: var(--border-thin) solid var(--color-line);
}
.media > img, .media > picture > img { width: 100%; height: 100%; object-fit: cover; }
.media--wide { aspect-ratio: 21 / 9; }
.media--4x3 { aspect-ratio: 4 / 3; }
.media--1x1 { aspect-ratio: 1 / 1; }
.media--tall { aspect-ratio: 3 / 4; }
.media__scrim { position: absolute; inset: 0; background: var(--overlay-scrim); }
.media__label {
  position: absolute;
  top: var(--space-2);
  left: var(--space-2);
  padding: 3px 10px;
  border: var(--border-thin) solid var(--color-contrast-accent);
  color: var(--color-contrast-accent);
  background-color: color-mix(in srgb, var(--color-contrast-surface) 65%, transparent);
  font-family: var(--font-mono);
  font-size: var(--text-xs);
  letter-spacing: 0.14em;
}
.media__body {
  position: absolute;
  inset: auto 0 0 0;
  padding: var(--space-4) var(--space-3) var(--space-3);
  color: var(--color-contrast-ink);
}
.media__body h2, .media__body h3 { color: var(--color-contrast-ink); }
.media__body p { max-width: 46ch; font-size: var(--text-sm); color: color-mix(in srgb, var(--color-contrast-ink) 86%, transparent); }
.media__caption {
  margin-top: var(--space-1);
  font-family: var(--font-mono);
  font-size: var(--text-xs);
  letter-spacing: 0.08em;
  color: var(--color-ink-muted);
}

/* ========== index list ========== */
.index-list { counter-reset: idx; border-top: 3px double var(--color-line); }
.index-list__item {
  position: relative;
  counter-increment: idx;
  padding: var(--space-3) 0 var(--space-3) 60px;
  border-bottom: var(--border-thin) solid var(--color-line);
}
.index-list__item::before {
  content: counter(idx, decimal-leading-zero);
  position: absolute;
  left: 0;
  top: calc(var(--space-3) + 0.3em);
  font-family: var(--font-mono);
  font-size: var(--text-sm);
  letter-spacing: 0.06em;
  color: var(--color-primary);
}
.index-list__title { font-family: var(--font-heading); font-size: var(--text-lg); }
.index-list__meta { display: block; margin-top: 4px; font-size: var(--text-sm); color: var(--color-ink-soft); }
.index-list__item:hover .index-list__title { color: var(--color-primary); }

/* ========== toc ========== */
.toc {
  position: sticky;
  top: 140px;
  padding: var(--space-3);
  border: 3px double var(--color-contrast-line);
  background-color: var(--color-contrast-surface);
  color: var(--color-contrast-ink);
}
.toc__title {
  padding-bottom: var(--space-2);
  margin-bottom: var(--space-2);
  border-bottom: var(--border-thin) solid var(--color-contrast-line);
  font-family: var(--font-mono);
  font-size: var(--text-xs);
  letter-spacing: 0.22em;
  color: var(--color-contrast-accent);
}
.toc__list { display: grid; gap: 2px; }
.toc__link {
  display: block;
  padding: 9px 10px;
  min-height: 40px;
  border-left: var(--border-thick) solid transparent;
  font-size: var(--text-sm);
  color: color-mix(in srgb, var(--color-contrast-ink) 78%, transparent);
  transition: color 0.2s ease, border-color 0.2s ease, background-color 0.2s ease;
}
.toc__link:hover { color: var(--color-contrast-ink); border-left-color: var(--color-contrast-line); }
.toc__link[aria-current="true"] {
  color: var(--color-contrast-accent);
  border-left-color: var(--color-contrast-accent);
  background-color: color-mix(in srgb, var(--color-contrast-accent) 12%, transparent);
}

/* ========== crumbs ========== */
.crumbs {
  padding-block: var(--space-2);
  border-bottom: var(--border-thin) solid var(--color-line);
  font-size: var(--text-xs);
  letter-spacing: 0.1em;
  color: var(--color-ink-muted);
}
.crumbs__list { display: flex; flex-wrap: wrap; align-items: center; gap: var(--space-2); }
.crumbs__list li { display: flex; align-items: center; gap: var(--space-2); }
.crumbs__list li + li::before { content: "／"; font-family: var(--font-mono); color: var(--color-primary); }
.crumbs a:hover { color: var(--color-primary); }
.crumbs [aria-current="page"] { color: var(--color-ink); }

/* ========== disclosure ========== */
.disclosure { border-bottom: var(--border-thin) solid var(--color-line); }
.disclosure__summary {
  display: flex;
  align-items: center;
  gap: var(--space-2);
  min-height: 44px;
  padding: var(--space-2) 0;
  cursor: pointer;
  font-family: var(--font-heading);
  font-size: var(--text-lg);
  letter-spacing: var(--tracking-heading);
  list-style: none;
}
.disclosure__summary::-webkit-details-marker { display: none; }
.disclosure__summary::before {
  content: "＋";
  font-family: var(--font-mono);
  font-size: var(--text-sm);
  color: var(--color-primary);
}
.disclosure[open] .disclosure__summary::before { content: "－"; }
.disclosure__body { padding: 0 0 var(--space-3) 30px; font-size: var(--text-sm); color: var(--color-ink-soft); }

/* ========== grids ========== */
.grid { display: grid; gap: var(--gutter); }
.grid--12 { grid-template-columns: repeat(12, minmax(0, 1fr)); }
.grid--2 { grid-template-columns: repeat(2, minmax(0, 1fr)); }
.grid--3 { grid-template-columns: repeat(3, minmax(0, 1fr)); }
.grid--7-5 { grid-template-columns: 7fr 5fr; }
.grid--5-7 { grid-template-columns: 5fr 7fr; }
.grid--8-4 { grid-template-columns: 8fr 4fr; }
.grid--4-8 { grid-template-columns: 4fr 8fr; }
.col-3 { grid-column: span 3; }
.col-4 { grid-column: span 4; }
.col-5 { grid-column: span 5; }
.col-6 { grid-column: span 6; }
.col-7 { grid-column: span 7; }
.col-8 { grid-column: span 8; }
.col-9 { grid-column: span 9; }
.col-12 { grid-column: span 12; }
.stack { display: grid; gap: var(--space-3); }
.stack--tight { gap: var(--space-1); }
.link-arrow { color: var(--color-ink); border-bottom: var(--border-thin) solid var(--color-line); }
.link-arrow::after { content: "→"; color: var(--color-primary); margin-left: 6px; font-family: var(--font-mono); }
.link-arrow:hover { border-bottom-color: var(--color-primary); color: var(--color-primary); }

/* ========== header ========== */
.site-header {
  position: sticky;
  top: 0;
  z-index: 60;
  background-color: var(--color-surface);
  border-bottom: 3px double var(--color-line);
}
.skip-link {
  position: absolute;
  left: var(--space-3);
  top: -120px;
  z-index: 120;
  padding: 10px var(--space-2);
  background-color: var(--color-primary);
  color: var(--color-primary-ink);
  font-size: var(--text-sm);
  letter-spacing: 0.12em;
  border-radius: var(--radius-sm);
  transition: top 0.2s ease;
}
.skip-link:focus { top: var(--space-1); }

.utility-bar {
  background-color: var(--color-surface-deep);
  border-bottom: var(--border-thin) solid var(--color-line);
  font-size: var(--text-xs);
  color: var(--color-ink-muted);
}
.utility-bar__inner {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: var(--space-2);
  min-height: 34px;
  letter-spacing: 0.14em;
}
.utility-bar__item { font-family: var(--font-mono); }
.utility-bar__item--region { color: var(--color-accent); }

.masthead { position: relative; background-color: var(--color-surface); }
.masthead__inner {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: var(--space-4);
  min-height: 80px;
}

.brand { display: flex; align-items: center; gap: var(--space-2); flex: 0 0 auto; }
.brand__mark {
  position: relative;
  display: grid;
  place-items: center;
  width: 46px;
  height: 46px;
  border: var(--border-thick) solid var(--color-primary);
  border-radius: var(--radius-sm);
  color: var(--color-primary);
  font-family: var(--font-heading);
  font-weight: var(--weight-heading);
  font-size: var(--text-lg);
  line-height: 1;
}
.brand__mark::after {
  content: "";
  position: absolute;
  inset: 3px;
  border: var(--border-thin) solid var(--color-line);
}
.brand__text { display: block; }
.brand__name {
  display: block;
  font-family: var(--font-heading);
  font-weight: var(--weight-heading);
  font-size: var(--text-lg);
  line-height: 1.2;
  letter-spacing: 0.18em;
  color: var(--color-ink);
}
.brand__sub {
  display: block;
  margin-top: 2px;
  font-family: var(--font-mono);
  font-size: var(--text-xs);
  letter-spacing: 0.2em;
  color: var(--color-ink-muted);
}

.site-nav { display: flex; align-items: center; gap: var(--space-3); }
.site-nav__list { display: flex; align-items: center; gap: var(--space-2); counter-reset: nav; }
.site-nav__list a {
  position: relative;
  display: inline-flex;
  align-items: center;
  gap: 6px;
  min-height: 44px;
  padding: 0 4px;
  font-size: var(--text-sm);
  letter-spacing: 0.08em;
  color: var(--color-ink);
  transition: color 0.2s ease;
}
.site-nav__list a::before {
  counter-increment: nav;
  content: counter(nav, decimal-leading-zero);
  font-family: var(--font-mono);
  font-size: var(--text-xs);
  letter-spacing: 0.02em;
  color: var(--color-ink-muted);
  transition: color 0.2s ease;
}
.site-nav__list a::after {
  content: "";
  position: absolute;
  left: 0;
  right: 0;
  bottom: 4px;
  border-bottom: 3px double transparent;
}
.site-nav__list a:hover { color: var(--color-primary); }
.site-nav__list a:hover::before { color: var(--color-primary); }
.site-nav__list a:hover::after { border-bottom-color: var(--color-primary); }
.site-nav__list a[aria-current="page"] { color: var(--color-primary); }
.site-nav__list a[aria-current="page"]::before { color: var(--color-primary); }
.site-nav__list a[aria-current="page"]::after { border-bottom-color: var(--color-primary); }
.site-nav__cta { flex: 0 0 auto; }

.nav-toggle {
  display: none;
  align-items: center;
  gap: var(--space-1);
  min-height: 44px;
  padding: 8px 12px;
  border: var(--border-thin) solid var(--color-line);
  border-radius: var(--radius-sm);
  color: var(--color-ink-soft);
  font-size: var(--text-xs);
  letter-spacing: 0.18em;
}
.nav-toggle__bars {
  position: relative;
  display: block;
  width: 18px;
  height: 11px;
  border-top: var(--border-thick) solid var(--color-ink);
  border-bottom: var(--border-thick) solid var(--color-ink);
}
.nav-toggle__bars::after {
  content: "";
  position: absolute;
  left: 0;
  right: 0;
  top: 50%;
  border-top: var(--border-thin) solid var(--color-primary);
}
.nav-toggle[aria-expanded="true"] { border-color: var(--color-primary); color: var(--color-primary); }

.scroll-progress { position: absolute; left: 0; right: 0; bottom: 0; height: 2px; pointer-events: none; }
.scroll-progress__bar {
  display: block;
  height: 100%;
  background-color: var(--color-accent);
  transform: scaleX(0);
  transform-origin: left center;
  transition: transform 0.12s linear;
}

/* ========== footer ========== */
.site-footer { background-color: var(--color-surface); }
.footer-transition {
  background-color: var(--color-surface-deep);
  border-top: var(--border-thin) solid var(--color-line);
  padding-block: 12px;
}
.meander {
  height: 8px;
  background-image:
    repeating-linear-gradient(90deg, var(--color-line) 0 1px, transparent 1px 8px),
    repeating-linear-gradient(90deg, transparent 0 4px, var(--color-accent) 4px 5px, transparent 5px 8px);
  background-repeat: repeat-x;
  background-size: 16px 8px, 16px 8px;
  background-position: 0 0, 0 6px;
}
.footer-insert {
  background-color: var(--color-contrast-surface);
  color: var(--color-contrast-ink);
  border-top: 3px double var(--color-contrast-line);
  padding-block: var(--space-8) var(--space-4);
}
.footer-main { display: block; }
.footer-grid { display: grid; grid-template-columns: 1.5fr 1fr 1fr 1fr; gap: var(--space-6) var(--space-4); }
.footer-col { min-width: 0; }
.footer-brand {
  font-family: var(--font-heading);
  font-size: var(--text-lg);
  font-weight: var(--weight-heading);
  letter-spacing: 0.2em;
  color: var(--color-contrast-ink);
}
.footer-slogan {
  margin-top: var(--space-1);
  max-width: 30ch;
  font-size: var(--text-sm);
  color: color-mix(in srgb, var(--color-contrast-ink) 76%, transparent);
}
.footer-col--brand .tag-row { margin-top: var(--space-3); }
.footer-heading {
  padding-bottom: var(--space-1);
  margin-bottom: var(--space-2);
  border-bottom: var(--border-thin) solid var(--color-contrast-line);
  font-family: var(--font-mono);
  font-size: var(--text-xs);
  font-weight: var(--weight-body);
  letter-spacing: 0.22em;
  color: var(--color-contrast-accent);
}
.footer-list { display: grid; gap: 10px; }
.footer-list a {
  display: inline-block;
  font-size: var(--text-sm);
  color: var(--color-contrast-ink);
  border-bottom: var(--border-thin) solid transparent;
  transition: color 0.2s ease, border-color 0.2s ease;
}
.footer-list a:hover { color: var(--color-contrast-accent); border-bottom-color: var(--color-contrast-accent); }

.footer-contact {
  display: grid;
  gap: 6px;
  margin-top: var(--space-6);
  padding: var(--space-4);
  border: 3px double var(--color-contrast-line);
}
.footer-contact__line { font-size: var(--text-sm); color: var(--color-contrast-ink); max-width: none; }
.footer-contact__value { font-family: var(--font-mono); color: var(--color-contrast-accent); letter-spacing: 0.02em; }
.footer-contact__note {
  margin-top: var(--space-1);
  font-size: var(--text-xs);
  color: color-mix(in srgb, var(--color-contrast-ink) 62%, transparent);
}
.footer-bottom {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: var(--space-3);
  flex-wrap: wrap;
  margin-top: var(--space-6);
  padding-top: var(--space-3);
  border-top: var(--border-thin) solid var(--color-contrast-line);
}
.footer-legal {
  font-family: var(--font-mono);
  font-size: var(--text-xs);
  letter-spacing: 0.08em;
  color: color-mix(in srgb, var(--color-contrast-ink) 70%, transparent);
  max-width: none;
}
.footer-policy { display: flex; flex-wrap: wrap; gap: var(--space-3); }
.footer-policy a { font-size: var(--text-xs); color: var(--color-contrast-ink); letter-spacing: 0.1em; }
.footer-policy a:hover { color: var(--color-contrast-accent); }

/* ========== back to top ========== */
.back-top {
  position: fixed;
  right: var(--space-3);
  bottom: var(--space-3);
  z-index: 70;
  display: none;
  place-items: center;
  width: 48px;
  height: 48px;
  border: 3px double var(--color-line);
  border-radius: var(--radius-sm);
  background-color: var(--color-surface);
  color: var(--color-ink-soft);
  font-family: var(--font-heading);
  font-size: var(--text-xs);
  letter-spacing: 0.2em;
  writing-mode: vertical-rl;
  transition: color 0.22s ease, border-color 0.22s ease, opacity 0.22s ease;
}
.back-top[data-visible] { display: grid; }
.back-top:hover { border-color: var(--color-primary); color: var(--color-primary); }

/* ========== reveal ========== */
.reveal { opacity: 0; transform: translateY(8px); transition: opacity 0.28s ease, transform 0.28s ease; }
.reveal.is-visible { opacity: 1; transform: none; }

/* ========== responsive ========== */
@media (max-width: 1100px) {
  .site-nav { gap: var(--space-2); }
  .site-nav__list { gap: var(--space-1); }
  .site-nav__list a { font-size: var(--text-xs); letter-spacing: 0.04em; }
  .brand__sub { letter-spacing: 0.12em; }
}
@media (max-width: 960px) {
  .grid--2, .grid--3, .grid--7-5, .grid--5-7, .grid--8-4, .grid--4-8 { grid-template-columns: minmax(0, 1fr); }
  .col-3, .col-4, .col-5, .col-6, .col-7, .col-8, .col-9 { grid-column: 1 / -1; }
  .stat-strip__grid { grid-template-columns: repeat(2, minmax(0, 1fr)); }
  .stat-strip__cell { padding: var(--space-2) var(--space-3); }
  .stat-strip__cell:nth-child(odd) { border-left: 0; padding-left: 0; }
  .stat-strip__cell:nth-child(n + 3) { border-top: var(--border-thin) solid var(--color-contrast-line); margin-top: var(--space-2); padding-top: var(--space-3); }
  .footer-grid { grid-template-columns: repeat(2, minmax(0, 1fr)); }
  .footer-col--brand { grid-column: 1 / -1; }
  .toc { position: static; top: auto; }
}
@media (max-width: 900px) {
  .nav-toggle { display: inline-flex; }
  .site-nav {
    display: none;
    position: absolute;
    left: 0;
    right: 0;
    top: 100%;
    z-index: 55;
    flex-direction: column;
    align-items: stretch;
    gap: var(--space-3);
    max-height: calc(100vh - 130px);
    overflow-y: auto;
    padding: var(--space-3) var(--space-3) var(--space-4);
    background-color: var(--color-surface);
    border-bottom: 3px double var(--color-line);
  }
  .site-header[data-open] .site-nav { display: flex; }
  .site-nav__list { flex-direction: column; align-items: stretch; gap: 0; }
  .site-nav__list li { border-bottom: var(--border-thin) dashed var(--color-line); }
  .site-nav__list li:first-child { border-top: var(--border-thin) dashed var(--color-line); }
  .site-nav__list a { width: 100%; justify-content: flex-start; padding: 14px 0; font-size: var(--text-sm); }
  .site-nav__list a::after { display: none; }
  .site-nav__list a[aria-current="page"] { border-bottom: 0; }
  .site-nav__cta { width: 100%; }
  .masthead__inner { min-height: 66px; }
}
@media (max-width: 620px) {
  .container { padding-inline: var(--space-2); }
  .section { padding-block: calc(var(--section-y) * 0.62); }
  .section--lg { padding-block: calc(var(--section-y-lg) * 0.6); }
  .section-head { grid-template-columns: minmax(0, 1fr); }
  .section-head__index { grid-row: auto; padding-top: 0; }
  .section-head__note, .section-head__actions { grid-column: 1; }
  .section-head--split { grid-template-columns: minmax(0, 1fr); }
  .section-head--split .section-head__actions { grid-column: 1; grid-row: auto; }
  .section-head__title { font-size: var(--text-2xl); }
  .footer-grid { grid-template-columns: minmax(0, 1fr); gap: var(--space-4); }
  .footer-contact { padding: var(--space-3); }
  .footer-bottom { flex-direction: column; align-items: flex-start; }
  .index-list__item { padding-left: 42px; }
  .media__body { padding: var(--space-3) var(--space-2) var(--space-2); }
  .brand__mark { width: 40px; height: 40px; }
  .brand__name { font-size: var(--text-base); letter-spacing: 0.12em; }
  .back-top { right: var(--space-2); bottom: var(--space-2); width: 44px; height: 44px; }
}

/* ========== reduced motion ========== */
@media (prefers-reduced-motion: reduce) {
  html { scroll-behavior: auto; }
  .reveal { opacity: 1; transform: none; transition: none; }
  .scroll-progress__bar { transition: none; }
  .spec-table tbody tr,
  .btn,
  .toc__link,
  .footer-list a,
  .back-top,
  .skip-link { transition: none; }
}