:root {
  --color-surface: #f9f9f9;
  --color-surface-alt: #f0f0f1;
  --color-surface-deep: #e4e4e5;
  --color-ink: #4d4752;
  --color-ink-soft: #736c7a;
  --color-ink-muted: #807986;
  --color-line: #dad9db;
  --color-primary: #8412ed;
  --color-primary-ink: #ffffff;
  --color-primary-soft: #e9d9f7;
  --color-accent: #9e6d15;
  --color-accent-ink: #ffffff;
  --color-highlight: #e9e0d0;
  --color-focus: #99660b;
  --color-contrast-surface: #22152f;
  --color-contrast-ink: #e6e4e7;
  --color-contrast-line: #4d4357;
  --color-contrast-accent: #e29c1d;
  --overlay-scrim: linear-gradient(180deg, rgba(34, 21, 47, 0.35) 0%, rgba(34, 21, 47, 0.72) 55%, rgba(34, 21, 47, 0.92) 100%);
  --font-heading: "Source Han Sans SC", "Noto Sans SC", SimHei, "Microsoft YaHei", sans-serif;
  --font-body: "PingFang SC", "Microsoft YaHei", "Source Han Sans SC", sans-serif;
  --font-mono: ui-monospace, Menlo, Consolas, monospace;
  --text-xs: 9.5px;
  --text-sm: 13.5px;
  --text-base: 16px;
  --text-lg: 22.6px;
  --text-xl: 32.0px;
  --text-2xl: 45.2px;
  --text-3xl: 64.0px;
  --text-4xl: 90.4px;
  --text-display: clamp(45px, 9.3vw, 119px);
  --text-figure: clamp(38px, 6.7vw, 86px);
  --weight-heading: 717;
  --weight-body: 400;
  --leading-body: 1.69;
  --leading-heading: 1.25;
  --tracking-heading: 0.007em;
  --radius-sm: 10px;
  --radius-md: 12px;
  --radius-lg: 14px;
  --radius-pill: 999px;
  --border-thin: 2px;
  --border-thick: 3px;
  --shadow-1: 0 1px 0 rgba(77, 71, 82, 0.12);
  --shadow-2: 0 2px 0 rgba(77, 71, 82, 0.18);
  --space-1: 8px;
  --space-2: 16px;
  --space-3: 24px;
  --space-4: 32px;
  --space-6: 48px;
  --space-8: 64px;
  --container: 1220px;
  --measure: 73ch;
  --gutter: 24px;
  --section-y: 76px;
  --section-y-lg: 106px;
}

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

html {
  -webkit-text-size-adjust: 100%;
  scroll-behavior: smooth;
  scroll-padding-top: 136px;
}

body {
  margin: 0;
  background: 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);
  -webkit-font-smoothing: antialiased;
}

body, h1, h2, h3, h4, h5, p, ul, ol, dl, figure, blockquote { margin: 0; }
ul, ol { list-style: none; padding: 0; }

img, svg, video { display: block; max-width: 100%; height: auto; }

a { color: inherit; text-decoration: none; }

button {
  font: inherit;
  color: inherit;
  background: none;
  border: 0;
  cursor: pointer;
}

a, button, [tabindex] { -webkit-tap-highlight-color: transparent; }
:focus { outline: none; }
:focus-visible {
  outline: var(--border-thick) solid var(--color-focus);
  outline-offset: 2px;
}

.skip-link {
  position: absolute;
  left: var(--space-2);
  top: var(--space-2);
  z-index: 200;
  transform: translateY(-260%);
  padding: var(--space-2) var(--space-3);
  background: var(--color-primary);
  color: var(--color-primary-ink);
  border-radius: var(--radius-sm);
  font-family: var(--font-heading);
  font-weight: var(--weight-heading);
  font-size: var(--text-sm);
}
.skip-link:focus { transform: translateY(0); }

/* ---------- typography ---------- */
h1, h2, h3, h4 {
  font-family: var(--font-heading);
  font-weight: var(--weight-heading);
  line-height: var(--leading-heading);
  letter-spacing: var(--tracking-heading);
  color: var(--color-ink);
}

.display {
  font-family: var(--font-heading);
  font-weight: var(--weight-heading);
  font-size: var(--text-display);
  line-height: 0.94;
  letter-spacing: -0.012em;
  color: var(--color-ink);
}

.mono, .num {
  font-family: var(--font-mono);
  font-variant-numeric: tabular-nums;
}

.lede {
  font-size: var(--text-lg);
  line-height: 1.5;
  color: var(--color-ink-soft);
  max-width: 46ch;
}

.kicker {
  display: inline-block;
  font-family: var(--font-mono);
  font-size: var(--text-xs);
  letter-spacing: 0.22em;
  text-transform: uppercase;
  color: var(--color-accent);
}

.prose { max-width: var(--measure); }
.prose--wide { max-width: none; }
.prose p { margin-bottom: var(--space-3); }
.prose p:last-child { margin-bottom: 0; }
.prose strong { font-weight: var(--weight-heading); }

/* ---------- layout ---------- */
.shell {
  width: 100%;
  max-width: var(--container);
  margin-inline: auto;
  padding-inline: var(--gutter);
}

.section {
  position: relative;
  padding-block: var(--section-y);
}
.section > .shell { position: relative; z-index: 1; }
.section--alt { background: var(--color-surface-alt); }
.section--deep { background: var(--color-surface-deep); }
.section--tall { padding-block: var(--section-y-lg); }

.section--dark {
  background: var(--color-contrast-surface);
  color: var(--color-contrast-ink);
}
.section--dark h1,
.section--dark h2,
.section--dark h3,
.section--dark h4 { color: var(--color-contrast-ink); }
.section--dark .lede { color: color-mix(in srgb, var(--color-contrast-ink) 78%, transparent); }
.section--dark .kicker { color: var(--color-contrast-accent); }
.section--dark .prose { color: color-mix(in srgb, var(--color-contrast-ink) 88%, transparent); }
.section--dark a:not(.btn):not(.nav-link):not(.nav-util) { color: var(--color-contrast-accent); }

/* 深色区块上沿的斜切色带：错位边界分隔语言 */
.section--dark::before {
  content: "";
  position: absolute;
  left: 0;
  top: calc(var(--space-2) * -1);
  width: min(42%, 520px);
  height: var(--space-2);
  background: var(--color-primary);
  clip-path: polygon(0 100%, 100% 0, 100% 100%);
  pointer-events: none;
}

/* ---------- chapter numbering ---------- */
.chapter { position: relative; }
.chapter__no {
  display: block;
  font-family: var(--font-mono);
  font-variant-numeric: tabular-nums;
  font-weight: var(--weight-heading);
  font-size: var(--text-figure);
  line-height: 0.84;
  letter-spacing: -0.02em;
  color: var(--color-primary);
}
.section--dark .chapter__no { color: var(--color-contrast-accent); }

.chapter__title {
  margin-top: var(--space-2);
  font-size: clamp(var(--text-xl), 4.6vw, var(--text-3xl));
}
.chapter__kicker {
  display: inline-block;
  margin-bottom: var(--space-2);
  padding: 4px var(--space-2);
  background: var(--color-accent);
  color: var(--color-accent-ink);
  border-radius: var(--radius-sm) var(--radius-sm) var(--radius-sm) 0;
  font-family: var(--font-mono);
  font-size: var(--text-xs);
  letter-spacing: 0.18em;
}
.chapter__note {
  margin-top: var(--space-2);
  max-width: var(--measure);
  color: var(--color-ink-soft);
}
.section--dark .chapter__note { color: color-mix(in srgb, var(--color-contrast-ink) 74%, transparent); }

/* ---------- header ---------- */
.site-header {
  position: sticky;
  top: 0;
  z-index: 60;
  background: var(--color-contrast-surface);
  color: var(--color-contrast-ink);
  border-bottom: var(--border-thick) solid var(--color-contrast-line);
}

.header-inner {
  display: flex;
  align-items: center;
  gap: var(--space-3);
  min-height: 68px;
  padding-block: var(--space-2);
}

.brand {
  display: flex;
  align-items: center;
  gap: var(--space-2);
  flex: 0 0 auto;
}
.brand-mark {
  display: grid;
  place-items: center;
  width: 46px;
  height: 46px;
  background: var(--color-primary);
  color: var(--color-primary-ink);
  border-radius: var(--radius-sm) var(--radius-sm) var(--radius-sm) 0;
  font-family: var(--font-mono);
  font-weight: var(--weight-heading);
  font-size: var(--text-sm);
  box-shadow: var(--shadow-2);
  transform: rotate(-4deg);
}
.brand-name {
  display: block;
  font-family: var(--font-heading);
  font-weight: var(--weight-heading);
  font-size: var(--text-base);
  letter-spacing: var(--tracking-heading);
}
.brand-sub {
  display: block;
  font-size: var(--text-xs);
  letter-spacing: 0.14em;
  color: color-mix(in srgb, var(--color-contrast-ink) 62%, transparent);
}

.site-nav {
  margin-left: auto;
  display: flex;
  align-items: center;
  gap: var(--space-3);
}
.nav-list {
  display: flex;
  align-items: center;
  gap: 4px;
}
.nav-link {
  display: block;
  padding: var(--space-1) var(--space-2);
  border-radius: var(--radius-sm);
  font-size: var(--text-sm);
  color: var(--color-contrast-ink);
  white-space: nowrap;
  transition: background-color 0.16s linear, color 0.16s linear;
}
.nav-link:hover { background: color-mix(in srgb, var(--color-contrast-ink) 14%, transparent); }
.nav-link[aria-current="page"] {
  background: var(--color-primary);
  color: var(--color-primary-ink);
  font-weight: var(--weight-heading);
}
.nav-utility {
  display: flex;
  align-items: center;
  gap: var(--space-1);
  padding-left: var(--space-3);
  border-left: var(--border-thin) solid var(--color-contrast-line);
}
.nav-util {
  padding: 5px var(--space-2);
  border: var(--border-thin) solid var(--color-contrast-line);
  border-radius: var(--radius-pill);
  font-size: var(--text-xs);
  letter-spacing: 0.08em;
  white-space: nowrap;
  color: color-mix(in srgb, var(--color-contrast-ink) 84%, transparent);
  transition: border-color 0.16s linear, color 0.16s linear;
}
.nav-util:hover {
  border-color: var(--color-contrast-accent);
  color: var(--color-contrast-accent);
}

.nav-toggle {
  display: none;
  margin-left: auto;
  align-items: center;
  gap: var(--space-1);
  padding: var(--space-1) var(--space-2);
  border: var(--border-thin) solid var(--color-contrast-line);
  border-radius: var(--radius-sm);
  color: var(--color-contrast-ink);
  font-size: var(--text-sm);
}
.nav-toggle-bars { display: grid; gap: 3px; width: 18px; }
.nav-toggle-bars i {
  display: block;
  height: 2px;
  border-radius: 2px;
  background: currentColor;
  transition: transform 0.16s linear, opacity 0.16s linear;
}
.site-header[data-open="true"] .nav-toggle-bars i:nth-child(1) { transform: translateY(5px) rotate(45deg); }
.site-header[data-open="true"] .nav-toggle-bars i:nth-child(2) { opacity: 0; }
.site-header[data-open="true"] .nav-toggle-bars i:nth-child(3) { transform: translateY(-5px) rotate(-45deg); }

.header-rail {
  background: color-mix(in srgb, var(--color-contrast-surface) 88%, var(--color-primary) 12%);
  border-top: var(--border-thin) solid var(--color-contrast-line);
}
.rail-inner {
  display: flex;
  align-items: center;
  gap: var(--space-3);
  min-height: 34px;
  font-family: var(--font-mono);
  font-size: var(--text-xs);
}
.clock-chip { display: inline-flex; align-items: center; gap: var(--space-2); }
.clock-dial {
  display: inline-grid;
  place-items: center;
  min-width: 44px;
  padding: 2px var(--space-1);
  background: var(--color-contrast-accent);
  color: var(--color-contrast-surface);
  border-radius: var(--radius-sm);
  font-weight: var(--weight-heading);
}
.clock-plus { font-size: 0.8em; vertical-align: super; }
.clock-label { letter-spacing: 0.14em; color: color-mix(in srgb, var(--color-contrast-ink) 78%, transparent); }
.clock-range { color: var(--color-contrast-accent); letter-spacing: 0.06em; }
.rail-note {
  margin-left: auto;
  letter-spacing: 0.06em;
  color: color-mix(in srgb, var(--color-contrast-ink) 52%, transparent);
}

/* ---------- footer ---------- */
.site-footer {
  position: relative;
  overflow: hidden;
  padding-top: var(--section-y-lg);
  background: var(--color-contrast-surface);
  color: var(--color-contrast-ink);
}

.footer-grid {
  display: grid;
  grid-template-columns: 1.1fr 1.7fr 1.2fr;
  gap: var(--space-6);
  align-items: start;
}
.footer-brand-name {
  font-family: var(--font-heading);
  font-weight: var(--weight-heading);
  font-size: var(--text-lg);
  letter-spacing: var(--tracking-heading);
}
.footer-closing {
  margin-top: var(--space-1);
  max-width: 30ch;
  color: color-mix(in srgb, var(--color-contrast-ink) 74%, transparent);
}
.footer-stamp {
  margin-top: var(--space-2);
  font-family: var(--font-mono);
  font-size: var(--text-xs);
  letter-spacing: 0.2em;
  color: var(--color-contrast-accent);
}

.footer-nav {
  display: grid;
  grid-template-columns: repeat(3, minmax(0, 1fr));
  gap: var(--space-3);
}
.footer-col-title {
  margin-bottom: var(--space-2);
  font-family: var(--font-heading);
  font-size: var(--text-sm);
  font-weight: var(--weight-heading);
  letter-spacing: 0.08em;
  color: var(--color-contrast-accent);
}
.footer-col ul { display: grid; gap: var(--space-1); }
.footer-col a {
  display: inline-block;
  padding-bottom: 1px;
  border-bottom: var(--border-thin) solid transparent;
  font-size: var(--text-sm);
  color: color-mix(in srgb, var(--color-contrast-ink) 90%, transparent);
  transition: color 0.16s linear, border-color 0.16s linear;
}
.footer-col a:hover {
  color: var(--color-contrast-accent);
  border-bottom-color: var(--color-contrast-accent);
}

.contact-list {
  display: grid;
  gap: var(--space-2);
  font-size: var(--text-sm);
  color: color-mix(in srgb, var(--color-contrast-ink) 86%, transparent);
}
.contact-list li { line-height: 1.5; overflow-wrap: anywhere; }
.contact-label {
  display: block;
  margin-bottom: 2px;
  font-family: var(--font-mono);
  font-size: var(--text-xs);
  letter-spacing: 0.16em;
  color: color-mix(in srgb, var(--color-contrast-ink) 52%, transparent);
}

.footer-word {
  display: flex;
  flex-direction: column;
  width: 100%;
  max-width: var(--container);
  margin: var(--space-6) auto 0;
  padding: var(--space-6) var(--gutter) var(--space-1);
  border-top: var(--border-thick) solid var(--color-contrast-line);
  font-family: var(--font-heading);
  font-weight: var(--weight-heading);
  font-size: clamp(var(--text-2xl), 13.5vw, calc(var(--text-4xl) * 1.5));
  line-height: 0.82;
  letter-spacing: -0.025em;
  text-transform: uppercase;
  color: var(--color-contrast-ink);
}
.footer-word span { display: block; }
.footer-word span:last-child {
  padding-left: 9%;
  color: var(--color-contrast-accent);
}

.footer-base {
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  justify-content: space-between;
  gap: var(--space-2);
  padding-block: var(--space-3);
  border-top: var(--border-thin) solid var(--color-contrast-line);
  font-family: var(--font-mono);
  font-size: var(--text-xs);
  letter-spacing: 0.1em;
  color: color-mix(in srgb, var(--color-contrast-ink) 68%, transparent);
}

/* ---------- buttons ---------- */
.btn {
  display: inline-flex;
  align-items: center;
  gap: var(--space-1);
  padding: var(--space-2) var(--space-3);
  border: var(--border-thin) solid var(--color-ink);
  border-radius: var(--radius-sm);
  background: var(--color-surface);
  color: var(--color-ink);
  font-family: var(--font-heading);
  font-weight: var(--weight-heading);
  font-size: var(--text-sm);
  letter-spacing: 0.02em;
  box-shadow: var(--shadow-1);
  transition: transform 0.16s linear, box-shadow 0.16s linear, background-color 0.16s linear, color 0.16s linear;
}
.btn:hover { transform: translate(-1px, -1px); box-shadow: var(--shadow-2); }
.btn--primary {
  background: var(--color-primary);
  border-color: var(--color-primary);
  color: var(--color-primary-ink);
}
.btn--accent {
  background: var(--color-accent);
  border-color: var(--color-accent);
  color: var(--color-accent-ink);
}
.btn--ghost { background: transparent; }
.section--dark .btn--ghost {
  border-color: var(--color-contrast-line);
  color: var(--color-contrast-ink);
  background: transparent;
}
.section--dark .btn--ghost:hover { border-color: var(--color-contrast-accent); color: var(--color-contrast-accent); }

/* ---------- badges / stamps ---------- */
.badge {
  display: inline-flex;
  align-items: center;
  gap: 6px;
  padding: 3px var(--space-2);
  border: var(--border-thin) solid var(--color-line);
  border-radius: var(--radius-pill);
  background: var(--color-surface-alt);
  font-family: var(--font-mono);
  font-size: var(--text-xs);
  letter-spacing: 0.08em;
  color: var(--color-ink-soft);
}
.badge--accent { background: var(--color-surface); border-color: var(--color-accent); color: var(--color-accent); }
.badge--primary { background: var(--color-primary); border-color: var(--color-primary); color: var(--color-primary-ink); }
.badge--live { background: var(--color-contrast-surface); border-color: var(--color-contrast-surface); color: var(--color-contrast-accent); }

.stamp-row {
  display: flex;
  flex-wrap: wrap;
  gap: var(--space-1) var(--space-3);
  font-family: var(--font-mono);
  font-size: var(--text-xs);
  letter-spacing: 0.06em;
  color: var(--color-ink-muted);
}
.section--dark .stamp-row { color: color-mix(in srgb, var(--color-contrast-ink) 62%, transparent); }

/* ---------- breadcrumb ---------- */
.breadcrumb {
  font-size: var(--text-sm);
  color: var(--color-ink-soft);
}
.breadcrumb ol {
  display: flex;
  flex-wrap: wrap;
  gap: var(--space-1);
}
.breadcrumb li { display: inline-flex; align-items: center; gap: var(--space-1); }
.breadcrumb li + li::before {
  content: "/";
  color: var(--color-ink-muted);
}
.breadcrumb a { border-bottom: var(--border-thin) solid var(--color-line); }
.breadcrumb a:hover { border-bottom-color: var(--color-primary); color: var(--color-primary); }

/* ---------- stats ---------- */
.stat-strip {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(180px, 1fr));
  gap: var(--space-3);
}
.stat-cell {
  padding: var(--space-3);
  background: var(--color-surface);
  border: var(--border-thin) solid var(--color-line);
  border-radius: var(--radius-md);
  box-shadow: var(--shadow-1);
}
.stat-value {
  display: block;
  font-family: var(--font-mono);
  font-variant-numeric: tabular-nums;
  font-weight: var(--weight-heading);
  font-size: clamp(var(--text-lg), 3vw, var(--text-2xl));
  line-height: 1;
  color: var(--color-primary);
}
.stat-label {
  display: block;
  margin-top: var(--space-1);
  font-size: var(--text-sm);
  color: var(--color-ink-soft);
}
.section--dark .stat-cell {
  background: color-mix(in srgb, var(--color-contrast-surface) 82%, var(--color-contrast-ink) 18%);
  border-color: var(--color-contrast-line);
  box-shadow: none;
}
.section--dark .stat-value { color: var(--color-contrast-accent); }
.section--dark .stat-label { color: color-mix(in srgb, var(--color-contrast-ink) 70%, transparent); }

/* ---------- tables ---------- */
.data-table {
  width: 100%;
  border-collapse: collapse;
  font-size: var(--text-sm);
}
.data-table caption {
  padding-bottom: var(--space-2);
  text-align: left;
  font-size: var(--text-sm);
  color: var(--color-ink-soft);
}
.data-table th,
.data-table td {
  padding: var(--space-2);
  text-align: left;
  vertical-align: top;
  border-bottom: var(--border-thin) solid var(--color-line);
}
.data-table thead th {
  background: var(--color-surface-deep);
  font-family: var(--font-heading);
  font-weight: var(--weight-heading);
  color: var(--color-ink);
  white-space: nowrap;
}
.data-table tbody tr:nth-child(even) { background: var(--color-highlight); }
.data-table tbody tr { transition: background-color 0.16s linear, box-shadow 0.16s linear; }
.data-table tbody tr:hover { background: var(--color-primary-soft); }
.data-table tbody tr.is-focus {
  background: var(--color-primary-soft);
  box-shadow: inset var(--border-thick) 0 0 var(--color-primary);
}
.data-table .num { white-space: nowrap; }

.section--dark .data-table { color: var(--color-contrast-ink); }
.section--dark .data-table th,
.section--dark .data-table td { border-bottom-color: var(--color-contrast-line); }
.section--dark .data-table thead th {
  background: color-mix(in srgb, var(--color-contrast-surface) 70%, var(--color-contrast-ink) 30%);
  color: var(--color-contrast-ink);
}
.section--dark .data-table tbody tr:nth-child(even) {
  background: color-mix(in srgb, var(--color-contrast-surface) 88%, var(--color-contrast-ink) 12%);
}
.section--dark .data-table tbody tr:hover,
.section--dark .data-table tbody tr.is-focus {
  background: color-mix(in srgb, var(--color-contrast-surface) 62%, var(--color-primary) 38%);
}

/* ---------- pulse number ---------- */
.num-pulse {
  display: inline-block;
  padding: 0 2px;
  border-radius: var(--radius-sm);
  transition: background-color 0.16s linear, box-shadow 0.16s linear;
}
.num-pulse.is-pulsed {
  background: var(--color-primary-soft);
  box-shadow: 0 0 0 var(--border-thick) var(--color-primary);
}
.section--dark .num-pulse.is-pulsed {
  background: color-mix(in srgb, var(--color-contrast-surface) 60%, var(--color-contrast-accent) 40%);
  box-shadow: 0 0 0 var(--border-thick) var(--color-contrast-accent);
}

/* ---------- chapter toc ---------- */
.toc {
  position: sticky;
  top: calc(var(--space-8) * 2);
  align-self: start;
}
.toc-title {
  margin-bottom: var(--space-2);
  font-family: var(--font-mono);
  font-size: var(--text-xs);
  letter-spacing: 0.2em;
  color: var(--color-ink-muted);
}
.toc-list { display: grid; gap: 4px; }
.toc-link {
  display: flex;
  align-items: baseline;
  gap: var(--space-2);
  padding: var(--space-1) var(--space-2);
  border-left: var(--border-thick) solid var(--color-line);
  border-radius: 0 var(--radius-sm) var(--radius-sm) 0;
  font-size: var(--text-sm);
  color: var(--color-ink-soft);
  transition: background-color 0.16s linear, color 0.16s linear, border-color 0.16s linear;
}
.toc-link:hover { background: var(--color-surface-alt); color: var(--color-ink); }
.toc-link.is-active {
  background: var(--color-primary-soft);
  border-left-color: var(--color-primary);
  color: var(--color-ink);
  font-weight: var(--weight-heading);
}
.toc-index {
  font-family: var(--font-mono);
  font-variant-numeric: tabular-nums;
  color: var(--color-primary);
}

/* ---------- media ---------- */
.media {
  position: relative;
  overflow: hidden;
  border: var(--border-thick) solid var(--color-line);
  border-radius: var(--radius-lg);
  background: var(--color-surface-deep);
  box-shadow: var(--shadow-1);
}
.media img,
.media__img {
  width: 100%;
  height: 100%;
  object-fit: cover;
  aspect-ratio: 16 / 9;
}
.media--wide img,
.media--wide .media__img { aspect-ratio: 21 / 9; }
.media--tall img,
.media--tall .media__img { aspect-ratio: 4 / 5; }
.media--square img,
.media--square .media__img { aspect-ratio: 1 / 1; }
.media--dark { border-color: var(--color-contrast-line); }
.media__scrim {
  position: absolute;
  inset: 0;
  background: var(--overlay-scrim);
  pointer-events: none;
}
.media__caption {
  position: absolute;
  left: var(--space-3);
  right: var(--space-3);
  bottom: var(--space-3);
  z-index: 1;
  font-size: var(--text-sm);
  line-height: 1.5;
  color: var(--color-contrast-ink);
}

/* ---------- decorative shapes ---------- */
.deco {
  position: absolute;
  z-index: 0;
  pointer-events: none;
}
.deco--dot {
  width: 88px;
  height: 88px;
  border-radius: 50%;
  background: var(--color-primary);
  opacity: 0.18;
}
.deco--bar {
  width: 140px;
  height: 22px;
  border-radius: var(--radius-pill);
  background: var(--color-accent);
  opacity: 0.55;
  transform: rotate(-8deg);
}
.deco--chip {
  width: 118px;
  height: 54px;
  border: var(--border-thick) solid var(--color-line);
  border-radius: var(--radius-md) var(--radius-md) var(--radius-md) 0;
  background: var(--color-surface-alt);
}
.deco--arc {
  width: 180px;
  height: 90px;
  border-radius: 180px 180px 0 0;
  background: var(--color-highlight);
}
.section--dark .deco--dot { background: var(--color-contrast-accent); opacity: 0.22; }
.section--dark .deco--chip { border-color: var(--color-contrast-line); background: transparent; }

/* ---------- back to top ---------- */
.to-top {
  position: fixed;
  right: var(--space-3);
  bottom: var(--space-3);
  z-index: 80;
  display: inline-flex;
  align-items: center;
  padding: var(--space-2) var(--space-3);
  background: var(--color-primary);
  color: var(--color-primary-ink);
  border: var(--border-thin) solid var(--color-primary);
  border-radius: var(--radius-sm) var(--radius-sm) var(--radius-sm) 0;
  font-family: var(--font-heading);
  font-weight: var(--weight-heading);
  font-size: var(--text-sm);
  box-shadow: var(--shadow-2);
  opacity: 0;
  visibility: hidden;
  transform: translateY(12px);
  transition: opacity 0.16s linear, transform 0.16s linear, visibility 0.16s linear;
}
.to-top.is-visible { opacity: 1; visibility: visible; transform: translateY(0); }

/* ---------- responsive ---------- */
@media (max-width: 1080px) {
  .footer-grid { grid-template-columns: 1fr 1fr; }
  .footer-contact { grid-column: 1 / -1; }
}

@media (max-width: 900px) {
  html { scroll-padding-top: 112px; }
  .nav-toggle { display: inline-flex; }

  .site-nav {
    position: absolute;
    inset: 100% 0 auto 0;
    display: grid;
    gap: var(--space-2);
    padding: var(--space-3) var(--gutter) var(--space-4);
    background: var(--color-contrast-surface);
    border-bottom: var(--border-thick) solid var(--color-primary);
    visibility: hidden;
    opacity: 0;
    transform: translateY(-8px);
    transition: opacity 0.16s linear, transform 0.16s linear, visibility 0.16s linear;
  }
  .site-header[data-open="true"] .site-nav {
    visibility: visible;
    opacity: 1;
    transform: translateY(0);
  }
  .nav-list { flex-direction: column; align-items: stretch; gap: 2px; }
  .nav-link {
    padding: var(--space-2);
    border-left: var(--border-thick) solid transparent;
    border-radius: 0;
    font-size: var(--text-base);
  }
  .nav-link[aria-current="page"] {
    border-left-color: var(--color-contrast-accent);
    background: var(--color-primary);
  }
  .nav-utility {
    flex-wrap: wrap;
    padding-left: 0;
    padding-top: var(--space-2);
    border-left: 0;
    border-top: var(--border-thin) solid var(--color-contrast-line);
  }
  .rail-note { display: none; }
  .toc { position: static; }
}

@media (max-width: 640px) {
  :root { --gutter: 18px; }
  .header-inner { min-height: 60px; }
  .brand-mark { width: 40px; height: 40px; }
  .brand-sub { display: none; }
  .rail-inner { gap: var(--space-2); font-size: var(--text-xs); }
  .section { padding-block: var(--space-6); }
  .footer-nav { grid-template-columns: 1fr 1fr; }
  .footer-base { flex-direction: column; align-items: flex-start; gap: var(--space-1); }
  .to-top { right: var(--space-2); bottom: var(--space-2); }
}

@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;
  }
  .btn:hover { transform: none; }
  .to-top { transform: none; }
  .site-nav { transform: none; }
}