:root {
  --color-surface: #f3f3f4;
  --color-surface-alt: #eaeaec;
  --color-surface-deep: #dedee0;
  --color-ink: #434451;
  --color-ink-soft: #676879;
  --color-ink-muted: #767889;
  --color-line: #d3d4d7;
  --color-primary: #2733d8;
  --color-primary-ink: #ffffff;
  --color-primary-soft: #d6d8f0;
  --color-accent: #4a8307;
  --color-accent-ink: #ffffff;
  --color-highlight: #d5dfc9;
  --color-focus: #427a00;
  --color-contrast-surface: #18192e;
  --color-contrast-ink: #e4e4e7;
  --color-contrast-line: #454657;
  --color-contrast-accent: #88f20d;
  --overlay-scrim: linear-gradient(180deg, rgba(24, 25, 46, 0.35) 0%, rgba(24, 25, 46, 0.72) 55%, rgba(24, 25, 46, 0.92) 100%);
  --font-heading: "Source Han Serif SC", "Songti SC", Georgia, serif;
  --font-body: "PingFang SC", "Hiragino Sans GB", "Microsoft YaHei", sans-serif;
  --font-mono: ui-monospace, Menlo, Consolas, monospace;
  --text-xs: 10.7px;
  --text-sm: 13.4px;
  --text-base: 15px;
  --text-lg: 18.8px;
  --text-xl: 23.4px;
  --text-2xl: 29.3px;
  --text-3xl: 36.6px;
  --text-4xl: 45.8px;
  --text-display: clamp(41px, 8.5vw, 109px);
  --text-figure: clamp(34px, 6.1vw, 78px);
  --weight-heading: 731;
  --weight-body: 400;
  --leading-body: 1.76;
  --leading-heading: 1.22;
  --tracking-heading: 0.002em;
  --radius-sm: 1px;
  --radius-md: 2px;
  --radius-lg: 2px;
  --radius-pill: 2px;
  --border-thin: 1px;
  --border-thick: 1px;
  --shadow-1: 0 1px 0 rgba(67, 68, 81, 0.12);
  --shadow-2: 0 2px 0 rgba(67, 68, 81, 0.18);
  --space-1: 6px;
  --space-2: 12px;
  --space-3: 18px;
  --space-4: 24px;
  --space-6: 36px;
  --space-8: 48px;
  --container: 1200px;
  --measure: 67ch;
  --gutter: 18px;
  --section-y: 91px;
  --section-y-lg: 127px;
}

/* =========================================================
   1. Reset
   ========================================================= */
*,
*::before,
*::after { box-sizing: border-box; }

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

body,
h1, h2, h3, h4, h5, h6,
p, figure, blockquote, dl, dd, ul, ol { margin: 0; }

ul, ol { list-style: none; padding: 0; }

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

button, input, select, textarea { font: inherit; color: inherit; }

button {
  background: none;
  border: 0;
  padding: 0;
  cursor: pointer;
}

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

table { border-collapse: collapse; width: 100%; }

/* =========================================================
   2. Base typography
   ========================================================= */
html, body { min-height: 100%; }

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);
  -webkit-font-smoothing: antialiased;
  overflow-x: hidden;
}

h1, h2, h3, h4, h5, h6 {
  font-family: var(--font-heading);
  font-weight: var(--weight-heading);
  line-height: var(--leading-heading);
  letter-spacing: var(--tracking-heading);
  color: var(--color-ink);
}

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 { text-wrap: pretty; }

main { display: block; }

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

:focus-visible {
  outline: 2px solid var(--color-focus);
  outline-offset: 2px;
}

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

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

.mono-label {
  font-size: var(--text-xs);
  letter-spacing: 0.14em;
  text-transform: uppercase;
  color: var(--color-ink-muted);
}

.mono-val { font-size: var(--text-sm); }

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

.metric-figure {
  font-family: var(--font-mono);
  font-variant-numeric: tabular-nums;
  font-size: var(--text-figure);
  font-weight: 600;
  line-height: 0.92;
  letter-spacing: -0.02em;
}

.kicker {
  display: inline-block;
  font-family: var(--font-mono);
  font-size: var(--text-xs);
  letter-spacing: 0.16em;
  text-transform: uppercase;
  color: var(--color-primary);
}

.lede {
  font-family: var(--font-heading);
  font-size: var(--text-lg);
  line-height: 1.62;
  color: var(--color-ink-soft);
}

.prose { max-width: var(--measure); }
.prose p + p { margin-top: var(--space-3); }

.prose--columns {
  max-width: none;
  columns: 2;
  column-gap: var(--space-6);
  column-rule: var(--border-thin) solid var(--color-line);
}

.prose--columns p { margin-bottom: var(--space-3); break-inside: avoid; }

.mark {
  background: var(--color-highlight);
  padding: 0 3px;
  box-decoration-break: clone;
}

.link-underline {
  position: relative;
  display: inline-block;
  color: var(--color-primary);
}

.link-underline::after {
  content: "";
  position: absolute;
  left: 0;
  right: 0;
  bottom: -2px;
  height: 2px;
  background: var(--color-accent);
  transform: scaleX(0);
  transform-origin: left center;
  transition: transform 260ms ease;
}

.link-underline:hover::after,
.link-underline:focus-visible::after,
.link-underline.is-on::after { transform: scaleX(1); }

.rule {
  border: 0;
  border-top: var(--border-thin) solid var(--color-line);
}

.rule--double {
  border: 0;
  border-top: 3px double var(--color-line);
}

/* =========================================================
   4. Layout helpers
   ========================================================= */
.section { padding-block: var(--section-y); }
.section--lg { padding-block: var(--section-y-lg); }

.section__head {
  display: flex;
  flex-wrap: wrap;
  align-items: baseline;
  justify-content: space-between;
  gap: var(--space-2);
  padding-bottom: var(--space-2);
  border-bottom: 3px double var(--color-line);
  margin-bottom: var(--space-6);
}

.grid {
  display: grid;
  grid-template-columns: repeat(12, minmax(0, 1fr));
  gap: var(--gutter);
}

.grid--split { grid-template-columns: repeat(12, minmax(0, 1fr)); }
.grid--split > .grid__main { grid-column: 1 / span 7; }
.grid--split > .grid__side { grid-column: 8 / span 5; }

/* =========================================================
   5. Cards, figures, buttons
   ========================================================= */
.card {
  background: var(--color-surface);
  border: var(--border-thin) solid var(--color-line);
  border-radius: var(--radius-md);
  padding: var(--space-4);
}

.card--dark {
  background: var(--color-contrast-surface);
  border-color: var(--color-contrast-line);
  color: var(--color-contrast-ink);
}

.card--dark h1,
.card--dark h2,
.card--dark h3,
.card--dark h4 { color: var(--color-contrast-ink); }

.figure {
  position: relative;
  display: block;
  width: 100%;
  overflow: hidden;
  background: var(--color-surface-alt);
  border: var(--border-thin) solid var(--color-line);
  border-radius: var(--radius-sm);
}

.figure > img {
  width: 100%;
  height: 100%;
  object-fit: cover;
}

.figure--wide { aspect-ratio: 16 / 9; }
.figure--tall { aspect-ratio: 3 / 4; }
.figure--square { aspect-ratio: 1 / 1; }
.figure--panel { aspect-ratio: 4 / 5; }

.figure__scrim {
  position: absolute;
  inset: 0;
  background: var(--overlay-scrim);
  pointer-events: none;
}

.figure__body {
  position: absolute;
  inset: auto 0 0 0;
  padding: var(--space-3);
  color: var(--color-contrast-ink);
  z-index: 1;
}

.figure__body h1,
.figure__body h2,
.figure__body h3 { color: var(--color-contrast-ink); }

.figure__caption {
  margin-top: var(--space-1);
  font-family: var(--font-mono);
  font-size: var(--text-xs);
  letter-spacing: 0.04em;
  color: var(--color-ink-muted);
}

.btn {
  display: inline-flex;
  align-items: center;
  gap: var(--space-1);
  padding: var(--space-2) var(--space-3);
  border: var(--border-thin) solid transparent;
  border-radius: var(--radius-sm);
  font-family: var(--font-body);
  font-size: var(--text-sm);
  letter-spacing: 0.06em;
  line-height: 1.2;
  cursor: pointer;
  transition: background-color 180ms ease, color 180ms ease, border-color 180ms ease;
}

.btn--primary {
  background: var(--color-primary);
  color: var(--color-primary-ink);
}
.btn--primary:hover { background: color-mix(in srgb, var(--color-primary) 84%, #000); }

.btn--accent {
  background: var(--color-accent);
  color: var(--color-accent-ink);
}
.btn--accent:hover { background: color-mix(in srgb, var(--color-accent) 84%, #000); }

.btn--ghost {
  background: transparent;
  border-color: var(--color-line);
  color: var(--color-ink);
}
.btn--ghost:hover {
  border-color: var(--color-primary);
  color: var(--color-primary);
}

.btn--contrast {
  background: var(--color-contrast-accent);
  color: var(--color-contrast-surface);
}
.btn--contrast:hover { background: color-mix(in srgb, var(--color-contrast-accent) 82%, #fff); }

/* =========================================================
   6. Breadcrumb & timeline skeleton
   ========================================================= */
.breadcrumb {
  font-family: var(--font-mono);
  font-size: var(--text-xs);
  letter-spacing: 0.06em;
  color: var(--color-ink-muted);
}

.breadcrumb ol {
  display: flex;
  flex-wrap: wrap;
  align-items: center;
}

.breadcrumb li { display: inline-flex; align-items: center; }

.breadcrumb li + li::before {
  content: "/";
  margin-inline: var(--space-1) var(--space-2);
  color: var(--color-line);
}

.breadcrumb a { color: var(--color-primary); }
.breadcrumb [aria-current="page"] { color: var(--color-ink-soft); }

.timeline {
  border-top: 3px double var(--color-line);
}

.timeline__item {
  display: grid;
  grid-template-columns: 108px minmax(0, 1fr);
  gap: var(--space-3);
  padding-block: var(--space-3);
  border-bottom: var(--border-thin) solid var(--color-line);
}

.timeline__stamp {
  font-family: var(--font-mono);
  font-size: var(--text-xs);
  letter-spacing: 0.1em;
  color: var(--color-primary);
  padding-top: 3px;
}

/* =========================================================
   7. Reveal motion
   ========================================================= */
html[data-js-ready] [data-reveal] {
  opacity: 0;
  transform: translateY(12px);
  transition: opacity 240ms ease, transform 240ms ease;
}

html[data-js-ready] [data-reveal].is-revealed {
  opacity: 1;
  transform: none;
}

/* =========================================================
   8. Header
   ========================================================= */
.site-header {
  position: relative;
  background: var(--color-surface);
  z-index: 30;
}

.skip-link {
  position: absolute;
  top: var(--space-1);
  left: 50%;
  transform: translate(-50%, -200%);
  z-index: 200;
  padding: var(--space-1) var(--space-3);
  background: var(--color-primary);
  color: var(--color-primary-ink);
  font-family: var(--font-mono);
  font-size: var(--text-xs);
  letter-spacing: 0.1em;
  border-radius: var(--radius-sm);
  transition: transform 180ms ease;
}

.skip-link:focus {
  transform: translate(-50%, 0);
}

/* --- top strip --- */
.top-strip {
  position: relative;
  background: var(--color-contrast-surface);
  color: var(--color-contrast-ink);
}

.top-strip__inner {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: var(--space-3);
  min-height: 28px;
  padding-block: 3px;
}

.top-strip__meta {
  display: flex;
  align-items: center;
  gap: var(--space-2);
  min-width: 0;
  font-family: var(--font-mono);
  font-size: var(--text-xs);
  letter-spacing: 0.06em;
  color: var(--color-contrast-ink);
  white-space: nowrap;
}

.top-strip__meta--right { justify-content: flex-end; }

.top-strip__key {
  color: var(--color-contrast-accent);
  letter-spacing: 0.14em;
}

.top-strip__sep { color: var(--color-contrast-line); }

.top-strip__meter {
  position: absolute;
  left: 0;
  bottom: 0;
  height: 2px;
  width: var(--meter, 0%);
  background: var(--color-contrast-accent);
  transition: width 120ms linear;
}

/* --- masthead --- */
.masthead {
  padding-block: var(--space-4) var(--space-3);
  background: var(--color-surface);
  border-bottom: var(--border-thin) solid var(--color-line);
}

.masthead__inner {
  display: grid;
  grid-template-columns: minmax(0, 1fr) auto minmax(0, 1fr);
  align-items: end;
  gap: var(--space-3);
}

.masthead__side {
  display: flex;
  align-items: center;
  gap: var(--space-3);
  min-width: 0;
  padding-bottom: var(--space-1);
  color: var(--color-ink-muted);
  font-size: var(--text-xs);
  letter-spacing: 0.12em;
  text-transform: uppercase;
}

.masthead__side--start { justify-content: flex-start; }
.masthead__side--end { justify-content: flex-end; flex-wrap: wrap; }

.masthead__brand {
  display: grid;
  justify-items: center;
  gap: 3px;
  text-align: center;
}

.masthead__brand-cn {
  font-family: var(--font-heading);
  font-weight: var(--weight-heading);
  font-size: clamp(var(--text-3xl), 5.4vw, calc(var(--text-4xl) * 1.35));
  line-height: 1;
  letter-spacing: 0.05em;
  color: var(--color-ink);
}

.masthead__brand-en {
  font-size: var(--text-xs);
  letter-spacing: 0.34em;
  color: var(--color-ink-muted);
}

.masthead__utility {
  display: inline-flex;
  gap: var(--space-3);
}

.utility-link {
  font-size: var(--text-sm);
  letter-spacing: 0.04em;
  color: var(--color-primary);
  border-bottom: var(--border-thin) solid currentColor;
  padding-bottom: 1px;
  transition: color 160ms ease, border-color 160ms ease;
}

.utility-link:hover,
.utility-link:focus-visible {
  color: var(--color-accent);
}

/* --- nav band --- */
.nav-band {
  background: var(--color-surface-alt);
  border-bottom: 3px double var(--color-line);
}

.nav-band__inner {
  display: flex;
  align-items: center;
  justify-content: center;
  padding-block: var(--space-1);
}

.nav-band__list {
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  justify-content: center;
  gap: 0 var(--space-4);
}

.nav-band__item { display: block; }

.nav-band__link {
  position: relative;
  display: inline-block;
  padding-block: var(--space-2) calc(var(--space-2) + 2px);
  font-size: var(--text-sm);
  letter-spacing: 0.14em;
  color: var(--color-ink-soft);
  transition: color 160ms ease;
}

.nav-band__link::after {
  content: "";
  position: absolute;
  left: 0;
  right: 0;
  bottom: 0;
  height: 2px;
  background: var(--color-primary);
  transform: scaleX(0);
  transform-origin: left center;
  transition: transform 260ms ease;
}

.nav-band__link:hover,
.nav-band__link:focus-visible { color: var(--color-ink); }

.nav-band__link:hover::after,
.nav-band__link:focus-visible::after { transform: scaleX(1); }

.nav-band__link[aria-current="page"] { color: var(--color-primary); }

.nav-band__link[aria-current="page"]::after { transform: scaleX(1); }

.nav-band__num {
  display: inline-block;
  margin-right: var(--space-1);
  font-family: var(--font-mono);
  font-variant-numeric: tabular-nums;
  font-size: var(--text-xs);
  color: var(--color-ink-muted);
}

.nav-toggle {
  display: none;
  align-items: center;
  gap: var(--space-1);
  padding: var(--space-1) var(--space-2);
  background: var(--color-surface);
  border: var(--border-thin) solid var(--color-line);
  border-radius: var(--radius-sm);
  font-family: var(--font-mono);
  font-size: var(--text-xs);
  letter-spacing: 0.12em;
  color: var(--color-ink);
}

.nav-toggle__bars {
  display: block;
  width: 12px;
  height: 8px;
  border-top: 1px solid var(--color-ink);
  border-bottom: 1px solid var(--color-ink);
}

.nav-toggle__text { line-height: 1; }

/* =========================================================
   9. Footer
   ========================================================= */
.site-footer {
  margin-top: var(--section-y);
  background: var(--color-contrast-surface);
  color: var(--color-contrast-ink);
  border-top: 3px double var(--color-contrast-line);
}

.site-footer__inner {
  padding-block: var(--space-8) var(--space-4);
}

.site-footer__brandline {
  display: flex;
  flex-wrap: wrap;
  align-items: baseline;
  justify-content: space-between;
  gap: var(--space-2);
  padding-bottom: var(--space-3);
}

.site-footer__brand {
  font-family: var(--font-heading);
  font-weight: var(--weight-heading);
  font-size: var(--text-xl);
  letter-spacing: 0.06em;
  color: var(--color-contrast-ink);
}

.site-footer__note {
  font-size: var(--text-xs);
  letter-spacing: 0.1em;
  color: color-mix(in srgb, var(--color-contrast-ink) 62%, transparent);
}

.site-footer__grid {
  display: grid;
  grid-template-columns: repeat(4, minmax(0, 1fr));
  border: var(--border-thin) solid var(--color-contrast-line);
}

.footer-panel {
  padding: var(--space-4);
  border-right: var(--border-thin) solid var(--color-contrast-line);
  min-width: 0;
}

.footer-panel:last-child { border-right: 0; }

.footer-panel__title {
  margin-bottom: var(--space-2);
  font-family: var(--font-mono);
  font-size: var(--text-sm);
  font-weight: 400;
  letter-spacing: 0.16em;
  color: var(--color-contrast-accent);
}

.footer-panel__text {
  font-size: var(--text-sm);
  line-height: 1.72;
  color: var(--color-contrast-ink);
}

.footer-panel__list {
  display: grid;
  gap: var(--space-1);
  font-size: var(--text-sm);
  line-height: 1.7;
  color: color-mix(in srgb, var(--color-contrast-ink) 86%, transparent);
}

.footer-panel__list a {
  color: var(--color-contrast-ink);
  border-bottom: var(--border-thin) solid var(--color-contrast-line);
  padding-bottom: 1px;
  transition: color 160ms ease, border-color 160ms ease;
}

.footer-panel__list a:hover,
.footer-panel__list a:focus-visible {
  color: var(--color-contrast-accent);
  border-color: var(--color-contrast-accent);
}

.site-footer__legal {
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  justify-content: space-between;
  gap: var(--space-2);
  margin-top: var(--space-4);
  padding-top: var(--space-3);
  border-top: var(--border-thin) solid var(--color-contrast-line);
  font-size: var(--text-xs);
  letter-spacing: 0.1em;
  color: color-mix(in srgb, var(--color-contrast-ink) 68%, transparent);
}

.site-footer :focus-visible,
.top-strip :focus-visible {
  outline-color: var(--color-contrast-accent);
}

/* =========================================================
   10. Responsive
   ========================================================= */
@media (max-width: 1000px) {
  .grid--split > .grid__main { grid-column: 1 / span 7; }
  .grid--split > .grid__side { grid-column: 8 / span 5; }
  .site-footer__grid { grid-template-columns: repeat(2, minmax(0, 1fr)); }
  .footer-panel:nth-child(2n) { border-right: 0; }
  .footer-panel:nth-child(-n + 2) { border-bottom: var(--border-thin) solid var(--color-contrast-line); }
}

@media (max-width: 900px) {
  .nav-band__list { max-width: 620px; gap: 0 var(--space-3); }
  .nav-band__link { font-size: var(--text-sm); letter-spacing: 0.1em; }
  .masthead__side { font-size: var(--text-xs); letter-spacing: 0.08em; }
  .prose--columns { columns: 1; column-rule: 0; }
}

@media (max-width: 860px) {
  .grid--split > .grid__main,
  .grid--split > .grid__side { grid-column: 1 / -1; }
}

@media (max-width: 760px) {
  .masthead { padding-block: var(--space-4) var(--space-3); }
  .masthead__inner {
    grid-template-columns: minmax(0, 1fr);
    justify-items: center;
    gap: var(--space-2);
  }
  .masthead__side { justify-content: center; padding-bottom: 0; }
  .masthead__brand-cn { letter-spacing: 0.04em; }
  .timeline__item { grid-template-columns: minmax(0, 1fr); gap: var(--space-1); }
}

@media (max-width: 720px) {
  .top-strip__inner { flex-wrap: wrap; row-gap: 2px; padding-block: var(--space-1); }
  .top-strip__meta { white-space: normal; }
  .top-strip__meta--right { justify-content: flex-start; }
}

@media (max-width: 640px) {
  .nav-band__inner {
    flex-direction: column;
    align-items: stretch;
    gap: var(--space-2);
    padding-block: var(--space-2);
  }
  .nav-toggle { display: inline-flex; align-self: center; }
  .nav-band__list {
    display: none;
    flex-direction: column;
    align-items: stretch;
    width: 100%;
    max-width: none;
    gap: 0;
    border-top: var(--border-thin) solid var(--color-line);
  }
  .nav-band[data-open] .nav-band__list { display: flex; }
  .nav-band__item { border-bottom: var(--border-thin) solid var(--color-line); }
  .nav-band__link { display: block; padding: var(--space-2) 0; }
  .nav-band__link::after { display: none; }
  .nav-band__link[aria-current="page"] {
    border-left: 3px solid var(--color-primary);
    padding-left: var(--space-2);
  }
  .site-footer__grid { grid-template-columns: minmax(0, 1fr); }
  .footer-panel { border-right: 0; border-bottom: var(--border-thin) solid var(--color-contrast-line); }
  .footer-panel:last-child { border-bottom: 0; }
  .site-footer__brandline { flex-direction: column; align-items: flex-start; }
  .section { padding-block: calc(var(--section-y) * 0.72); }
  .section--lg { padding-block: calc(var(--section-y-lg) * 0.68); }
}

@media (max-width: 420px) {
  .top-strip__meta--right { font-size: var(--text-xs); }
  .masthead__utility { gap: var(--space-2); }
}

/* =========================================================
   11. Reduced motion
   ========================================================= */
@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;
  }

  html[data-js-ready] [data-reveal] {
    opacity: 1;
    transform: none;
  }

  .top-strip__meter { transition: none; }
}