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

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

body {
  margin: 0;
  background: var(--paper);
  color: var(--ink);
  font-family: var(--font-sans);
  font-size: 17px;
  line-height: 1.75;
  -webkit-font-smoothing: antialiased;
  text-rendering: optimizeLegibility;
}

img, svg, video { display: block; max-width: 100%; }
button, input, select, textarea { font: inherit; color: inherit; }
p { margin: 0 0 1em; }
p:last-child { margin-bottom: 0; }
[hidden] { display: none !important; }

/* ========== 2. tokens ========== */
:root {
  --night: #0B1B2B;
  --night-2: #14314D;
  --teal: #14776B;
  --teal-soft: #58A79B;
  --orange: #F2762E;
  --orange-deep: #C24E14;
  --paper: #F5F1E8;
  --mid: #E4DED2;
  --line: #C3CDD2;
  --ink: #131C24;
  --num-light: #DCE9EC;
  --alert: #B3261E;

  --font-sans: "Noto Sans SC", "Source Han Sans SC", "PingFang SC", "Hiragino Sans GB", "Microsoft YaHei", system-ui, -apple-system, sans-serif;
  --font-mono: "JetBrains Mono", "IBM Plex Mono", ui-monospace, SFMono-Regular, Menlo, Consolas, monospace;

  --shell-max: 1280px;
  --gutter: clamp(16px, 4vw, 48px);
  --anchor-offset: 132px;
}

/* ========== 3. base type ========== */
h1, h2, h3, h4, h5 {
  margin: 0 0 .5em;
  font-weight: 900;
  letter-spacing: -.02em;
  line-height: 1.2;
  color: var(--ink);
}
h1 { font-size: clamp(30px, 5vw, 54px); }
h2 { font-size: clamp(24px, 3.4vw, 38px); }
h3 { font-size: clamp(18px, 2vw, 24px); letter-spacing: -.01em; }
h4 { font-size: 17px; letter-spacing: 0; }

a {
  color: var(--teal);
  text-decoration-thickness: 1px;
  text-underline-offset: .2em;
}
a:hover { color: var(--orange-deep); }

[id] { scroll-margin-top: var(--anchor-offset); }
#main-content { scroll-margin-top: var(--anchor-offset); outline: none; }

/* ========== 4. utilities ========== */
.shell {
  width: 100%;
  max-width: var(--shell-max);
  margin-inline: auto;
  padding-inline: var(--gutter);
}

.num {
  font-family: var(--font-mono);
  font-variant-numeric: tabular-nums;
  letter-spacing: .02em;
}

.coord {
  display: inline-block;
  font-family: var(--font-mono);
  font-size: 11px;
  letter-spacing: .16em;
  color: var(--teal);
  text-transform: uppercase;
}
.coord--light { color: var(--teal-soft); }

.side-note {
  display: inline-block;
  writing-mode: vertical-rl;
  text-orientation: mixed;
  font-size: 11px;
  letter-spacing: .24em;
  color: var(--teal);
  line-height: 1;
  flex: none;
}

.blueprint {
  background-image:
    linear-gradient(to right, rgba(195, 205, 210, .34) 1px, transparent 1px),
    linear-gradient(to bottom, rgba(195, 205, 210, .34) 1px, transparent 1px);
  background-size: 48px 48px;
  background-position: -1px -1px;
}

/* ========== 5. skip link ========== */
.skip-link {
  position: fixed;
  top: -120px;
  left: 16px;
  z-index: 300;
  padding: 12px 20px;
  background: var(--orange);
  color: var(--night);
  font-size: 14px;
  font-weight: 700;
  letter-spacing: .04em;
  text-decoration: none;
  border-radius: 0;
  transition: top .16s linear;
}
.skip-link:focus { top: 16px; color: var(--night); }

/* ========== 6. header ========== */
.site-header {
  position: sticky;
  top: 0;
  z-index: 120;
  background: var(--paper);
  border-bottom: 1px solid var(--line);
}

/* 6.1 上层：深夜蓝品牌带 */
.header-top {
  background: var(--night);
  color: var(--num-light);
  border-bottom: 1px solid rgba(88, 167, 155, .28);
}
.header-top__inner {
  display: flex;
  align-items: center;
  justify-content: space-between;
  flex-wrap: wrap;
  gap: 10px 28px;
  min-height: 58px;
  padding-block: 10px;
}

.brand {
  display: inline-flex;
  align-items: center;
  gap: 12px;
  text-decoration: none;
  color: var(--num-light);
}
.brand:hover { color: var(--paper); }
.brand__mark {
  display: grid;
  place-items: center;
  width: 34px;
  height: 34px;
  flex: none;
  background: var(--orange);
  color: var(--night);
  font-size: 17px;
  font-weight: 900;
  letter-spacing: -.04em;
  line-height: 1;
}
.brand__text { display: flex; flex-direction: column; line-height: 1.28; }
.brand__name {
  font-size: 17px;
  font-weight: 900;
  letter-spacing: .06em;
  color: var(--paper);
}
.brand__line {
  font-size: 11px;
  letter-spacing: .22em;
  color: var(--teal-soft);
}

.utility {
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  gap: 8px 22px;
  margin: 0;
  padding: 0;
  list-style: none;
}
.utility__link {
  display: inline-flex;
  align-items: center;
  padding-bottom: 2px;
  font-size: 12px;
  letter-spacing: .1em;
  color: var(--num-light);
  text-decoration: none;
  border-bottom: 1px solid transparent;
  transition: color .15s linear, border-color .15s linear;
}
.utility__link:hover {
  color: #FFFFFF;
  border-bottom-color: var(--teal-soft);
}
.utility__link--signal { color: var(--orange); }
.utility__link--signal::before {
  content: "";
  width: 6px;
  height: 6px;
  margin-right: 8px;
  background: var(--orange);
  flex: none;
}
.utility__link--signal:hover { color: var(--orange); border-bottom-color: var(--orange); }

/* 6.2 下层：栏目导航带 */
.header-main {
  background: var(--paper);
  border-bottom: 2px solid var(--teal);
}
.header-main__inner {
  display: flex;
  align-items: center;
  gap: 18px;
  min-height: 64px;
}

.nav-toggle {
  display: inline-flex;
  align-items: center;
  gap: 9px;
  padding: 10px 14px;
  background: transparent;
  border: 1px solid var(--line);
  border-radius: 0;
  color: var(--ink);
  font-size: 12px;
  letter-spacing: .12em;
  cursor: pointer;
  transition: border-color .15s linear, color .15s linear;
}
.nav-toggle:hover { border-color: var(--teal); color: var(--teal); }
.nav-toggle__bars { position: relative; width: 16px; height: 10px; flex: none; }
.nav-toggle__bars::before,
.nav-toggle__bars::after {
  content: "";
  position: absolute;
  left: 0;
  right: 0;
  height: 2px;
  background: currentColor;
}
.nav-toggle__bars::before { top: 0; }
.nav-toggle__bars::after { bottom: 0; }
.nav-toggle__label { line-height: 1; }

.primary-nav { display: none; }
.primary-nav__list { margin: 0; padding: 0; list-style: none; }
.primary-nav__link {
  display: block;
  color: var(--ink);
  text-decoration: none;
}

.header-tools {
  display: flex;
  align-items: center;
  gap: 8px;
  margin-left: auto;
}

.tool {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  gap: 8px;
  min-height: 38px;
  padding: 8px 13px;
  background: var(--paper);
  border: 1px solid var(--line);
  border-radius: 0;
  color: var(--ink);
  font-size: 12px;
  letter-spacing: .1em;
  line-height: 1.2;
  cursor: pointer;
  transition: border-color .15s linear, color .15s linear, background-color .15s linear;
}
.tool:hover { border-color: var(--teal); color: var(--teal); }
.tool[aria-expanded="true"] {
  background: var(--night);
  border-color: var(--night);
  color: var(--num-light);
}
.tool--top { color: var(--orange-deep); border-color: rgba(242, 118, 46, .5); }
.tool--top:hover { background: var(--orange); border-color: var(--orange); color: var(--night); }

/* 6.3 目录抽屉 */
.toc {
  background: var(--mid);
  border-top: 1px solid var(--line);
}
.toc__inner { padding-block: 18px 24px; }
.toc__label {
  margin: 0 0 10px;
  font-size: 11px;
  letter-spacing: .24em;
  color: var(--teal);
}
.toc__list {
  margin: 0;
  padding: 0;
  list-style: none;
  counter-reset: toc;
  display: grid;
  gap: 0;
}
.toc__list li { counter-increment: toc; }
.toc__link {
  display: flex;
  align-items: baseline;
  gap: 12px;
  width: 100%;
  padding: 9px 2px;
  background: transparent;
  border: 0;
  border-bottom: 1px solid rgba(195, 205, 210, .8);
  border-radius: 0;
  color: var(--ink);
  font-family: inherit;
  font-size: 14px;
  text-align: left;
  cursor: pointer;
  transition: color .12s linear, padding-left .12s linear;
}
.toc__link::before {
  content: counter(toc, decimal-leading-zero);
  flex: none;
  font-family: var(--font-mono);
  font-size: 11px;
  letter-spacing: .06em;
  color: var(--teal);
}
.toc__link:hover { color: var(--teal); padding-left: 8px; }
.toc__link--active { color: var(--orange-deep); }
.toc__link--active::before { color: var(--orange-deep); }

/* ========== 7. footer ========== */
.site-footer {
  background: var(--night);
  color: var(--num-light);
  border-top: 2px solid var(--teal);
}
.footer-grid {
  display: grid;
  grid-template-columns: 1fr;
  gap: 30px;
  padding-block: 56px 40px;
}
.footer-col {
  padding-top: 16px;
  border-top: 1px solid rgba(88, 167, 155, .42);
}
.footer-col--brand { border-top-color: var(--teal-soft); }

.footer-brand {
  margin: 0;
  font-size: 24px;
  font-weight: 900;
  letter-spacing: .08em;
  color: var(--paper);
  line-height: 1.2;
}
.footer-tagline {
  margin: 8px 0 14px;
  font-size: 12px;
  letter-spacing: .24em;
  color: var(--teal-soft);
}
.footer-note {
  margin: 0;
  max-width: 30ch;
  font-size: 13px;
  line-height: 1.8;
  color: rgba(220, 233, 236, .72);
}

.footer-heading {
  margin: 0 0 12px;
  font-size: 11px;
  font-weight: 700;
  letter-spacing: .24em;
  color: var(--teal-soft);
}
.footer-list {
  margin: 0;
  padding: 0;
  list-style: none;
  display: grid;
  gap: 9px;
}
.footer-list a {
  font-size: 14px;
  color: rgba(220, 233, 236, .86);
  text-decoration: none;
  border-bottom: 1px solid transparent;
  transition: color .15s linear, border-color .15s linear;
}
.footer-list a:hover {
  color: var(--orange);
  border-bottom-color: var(--orange);
}

.footer-contact p {
  margin: 0 0 8px;
  font-size: 13px;
  line-height: 1.72;
  color: rgba(220, 233, 236, .8);
}
.footer-contact .num { color: var(--paper); letter-spacing: .04em; }

.footer-bar {
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  justify-content: space-between;
  gap: 12px 24px;
  padding-block: 18px 26px;
  border-top: 1px solid rgba(195, 205, 210, .22);
  font-size: 12px;
}
.footer-bar p { margin: 0; color: rgba(220, 233, 236, .62); }
.footer-legal {
  display: flex;
  flex-wrap: wrap;
  gap: 8px 20px;
  margin: 0;
  padding: 0;
  list-style: none;
}
.footer-legal a {
  color: rgba(220, 233, 236, .76);
  text-decoration: none;
}
.footer-legal a:hover { color: var(--orange); }

/* ========== 8. buttons ========== */
.btn {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  gap: .5em;
  min-height: 44px;
  padding: 11px 24px;
  background: var(--orange);
  border: 1px solid var(--orange-deep);
  border-radius: 0;
  color: var(--night);
  font-size: 14px;
  font-weight: 700;
  letter-spacing: .08em;
  text-decoration: none;
  cursor: pointer;
  transition: background-color .15s linear, border-color .15s linear, color .15s linear;
}
.btn:hover {
  background: var(--orange-deep);
  border-color: var(--orange-deep);
  color: var(--paper);
}
.btn--ghost {
  background: transparent;
  border-color: var(--line);
  color: var(--ink);
  font-weight: 600;
}
.btn--ghost:hover {
  background: transparent;
  border-color: var(--teal);
  color: var(--teal);
}
.btn--night {
  background: var(--night);
  border-color: var(--night);
  color: var(--num-light);
}
.btn--night:hover {
  background: var(--night-2);
  border-color: var(--teal-soft);
  color: var(--paper);
}

/* ========== 9. breadcrumb ========== */
.breadcrumb {
  padding-block: 14px;
  border-bottom: 1px solid var(--line);
  font-size: 12px;
  letter-spacing: .06em;
  color: rgba(19, 28, 36, .62);
}
.breadcrumb ol {
  display: flex;
  flex-wrap: wrap;
  gap: 8px;
  margin: 0;
  padding: 0;
  list-style: none;
}
.breadcrumb li + li::before {
  content: "/";
  margin-right: 8px;
  color: var(--line);
}
.breadcrumb a { color: var(--teal); text-decoration: none; }
.breadcrumb a:hover { color: var(--orange-deep); }

/* ========== 10. page containers ========== */
.page { display: block; }

.section {
  padding-block: clamp(40px, 6vw, 88px);
  border-bottom: 1px solid var(--line);
}
.section--narrow {
  background: var(--mid);
  border-block: 1px solid var(--line);
}
.section--night {
  background: var(--night);
  color: var(--num-light);
  border-block: 1px solid var(--night-2);
}
.section--night h1,
.section--night h2,
.section--night h3,
.section--night h4 { color: var(--paper); }
.section--night a { color: var(--teal-soft); }
.section--night a:hover { color: var(--orange); }
.section--night .coord { color: var(--teal-soft); }
.section--night .side-note { color: var(--teal-soft); }

.section--teal {
  background: var(--teal);
  color: var(--paper);
  border-block: 1px solid rgba(11, 27, 43, .25);
}
.section--teal h1,
.section--teal h2,
.section--teal h3 { color: var(--paper); }
.section--teal a { color: var(--paper); }
.section--teal .coord,
.section--teal .side-note { color: var(--num-light); }

.prose { max-width: 68ch; }
.prose p { margin-bottom: 1.1em; }
.prose h2 { margin-top: 1.6em; }
.prose h3 { margin-top: 1.4em; }
.prose ul,
.prose ol { padding-left: 1.3em; margin: 0 0 1.2em; }
.prose li { margin-bottom: .4em; }

/* ========== 11. grids ========== */
.split {
  display: grid;
  grid-template-columns: 1fr;
  gap: 32px;
  align-items: start;
}
.split--reverse > :first-child { order: 2; }

/* ========== 12. section head ========== */
.section-head {
  display: flex;
  align-items: flex-start;
  gap: 16px;
  margin-bottom: 30px;
  padding-top: 14px;
  border-top: 1px solid var(--line);
}
.section--night .section-head,
.section--teal .section-head { border-top-color: rgba(195, 205, 210, .32); }

.section-title {
  margin: 0;
  font-size: clamp(24px, 3.4vw, 40px);
  font-weight: 900;
  letter-spacing: -.02em;
  line-height: 1.14;
}
.section-head__body { flex: 1 1 auto; min-width: 0; }
.section-head__meta {
  margin: .6em 0 0;
  font-size: 13px;
  letter-spacing: .04em;
  color: rgba(19, 28, 36, .68);
}
.section--night .section-head__meta { color: rgba(220, 233, 236, .7); }

/* ========== 13. card ========== */
.card {
  border: 1px solid var(--line);
  background: var(--paper);
  border-radius: 0;
  transition: border-color .16s linear;
}
.card:hover { border-color: var(--teal); }

.card__head {
  display: flex;
  align-items: baseline;
  justify-content: space-between;
  flex-wrap: wrap;
  gap: 8px 14px;
  padding: 12px 16px;
  border-bottom: 1px solid var(--line);
  font-family: var(--font-mono);
  font-size: 12px;
  letter-spacing: .06em;
  color: rgba(19, 28, 36, .72);
}
.card__body { padding: 18px 16px; }
.card__foot {
  padding: 12px 16px;
  border-top: 1px solid var(--line);
  font-size: 13px;
  line-height: 1.7;
  color: rgba(19, 28, 36, .72);
}

.card--night {
  background: var(--night-2);
  border-color: rgba(88, 167, 155, .45);
  color: var(--num-light);
}
.card--night .card__head {
  border-bottom-color: rgba(88, 167, 155, .4);
  color: var(--teal-soft);
}
.card--night .card__foot {
  border-top-color: rgba(88, 167, 155, .4);
  color: rgba(220, 233, 236, .72);
}
.card--night:hover { border-color: var(--orange); }

/* ========== 14. tag ========== */
.tag {
  display: inline-flex;
  align-items: center;
  gap: 6px;
  padding: 3px 9px;
  border: 1px solid currentColor;
  border-radius: 0;
  font-size: 11px;
  letter-spacing: .12em;
  line-height: 1.5;
  white-space: nowrap;
}
.tag--signal {
  color: var(--orange-deep);
  border-color: var(--orange);
  background: rgba(242, 118, 46, .12);
}
.tag--teal {
  color: var(--teal);
  border-color: var(--teal-soft);
  background: rgba(88, 167, 155, .12);
}
.tag--alert { color: var(--alert); border-color: var(--alert); }
.tag--alert::before {
  content: "";
  width: 6px;
  height: 6px;
  background: var(--alert);
  flex: none;
}

/* ========== 15. figure ========== */
.figure {
  margin: 0;
  border: 1px solid var(--line);
  background: var(--mid);
  border-radius: 0;
  overflow: hidden;
}
.figure__media {
  position: relative;
  width: 100%;
  aspect-ratio: 16 / 9;
  overflow: hidden;
  background: linear-gradient(135deg, var(--night-2) 0%, var(--teal) 58%, var(--night) 100%);
}
.figure__media--wide { aspect-ratio: 21 / 9; }
.figure__media--tall { aspect-ratio: 3 / 4; }
.figure__media img {
  width: 100%;
  height: 100%;
  object-fit: cover;
  display: block;
}
.figure__cap {
  padding: 10px 14px;
  border-top: 1px solid var(--line);
  font-size: 12px;
  line-height: 1.6;
  color: rgba(19, 28, 36, .7);
}

/* ========== 16. fold ========== */
.fold {
  border: 1px solid var(--line);
  background: var(--paper);
  border-radius: 0;
}
.fold + .fold { border-top: none; }
.fold__head {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 12px;
  width: 100%;
  padding: 14px 16px;
  background: var(--mid);
  border: 0;
  border-radius: 0;
  color: var(--ink);
  font-family: inherit;
  font-size: 14px;
  font-weight: 700;
  text-align: left;
  cursor: pointer;
  transition: background-color .14s linear, color .14s linear;
}
.fold__head:hover { background: #DCD5C7; color: var(--teal); }
.fold__head::after {
  content: "+";
  flex: none;
  font-family: var(--font-mono);
  font-size: 16px;
  color: var(--teal);
}
.fold__head[aria-expanded="true"]::after { content: "−"; color: var(--orange-deep); }
.fold__panel {
  padding: 16px;
  border-top: 1px solid var(--line);
  font-size: 15px;
}

/* ========== 17. focus & motion ========== */
:focus-visible {
  outline: 2px solid var(--teal);
  outline-offset: 2px;
}
.section--night :focus-visible,
.section--teal :focus-visible,
.site-footer :focus-visible,
.header-top :focus-visible {
  outline-color: var(--orange);
}

@media (prefers-reduced-motion: reduce) {
  html { scroll-behavior: auto; }
  *,
  *::before,
  *::after {
    animation-duration: .001ms !important;
    animation-iteration-count: 1 !important;
    transition-duration: .001ms !important;
    scroll-behavior: auto !important;
  }
}

/* ========== 18. responsive ========== */
@media (max-width: 899px) {
  .header-main__inner {
    flex-wrap: wrap;
    gap: 10px;
    padding-block: 10px;
  }
  .nav-toggle { order: 1; }
  .header-tools { order: 2; margin-left: auto; }
  .primary-nav {
    order: 3;
    flex: 1 1 100%;
    display: none;
  }
  .primary-nav[data-open] { display: block; }
  .primary-nav__link {
    padding: 14px 4px;
    font-size: 16px;
    border-top: 1px solid var(--line);
  }
  .primary-nav__link:hover { color: var(--teal); }
  .primary-nav__link[aria-current="page"] {
    color: var(--orange-deep);
    border-left: 3px solid var(--orange);
    padding-left: 11px;
  }
  .tool { font-size: 11px; padding: 8px 10px; letter-spacing: .06em; }
}

@media (max-width: 560px) {
  body { font-size: 16px; }
  .header-top__inner { gap: 10px 16px; }
  .utility { gap: 6px 14px; }
  .utility__link { font-size: 11px; }
  .brand__name { font-size: 15px; }
  .brand__line { font-size: 10px; letter-spacing: .18em; }
  .footer-bar { flex-direction: column; align-items: flex-start; }
}

@media (min-width: 640px) {
  .footer-grid { grid-template-columns: repeat(2, minmax(0, 1fr)); }
}

@media (min-width: 900px) {
  .nav-toggle { display: none; }
  .header-main__inner { flex-wrap: nowrap; }
  .primary-nav { display: block; flex: 1 1 auto; }
  .primary-nav__list { display: flex; align-items: stretch; gap: 2px; }
  .primary-nav__link {
    padding: 21px 14px;
    font-size: 14px;
    letter-spacing: .05em;
    border-bottom: 2px solid transparent;
    transition: color .15s linear, border-color .15s linear;
  }
  .primary-nav__link:hover { color: var(--teal); border-bottom-color: var(--teal-soft); }
  .primary-nav__link[aria-current="page"] {
    color: var(--teal);
    border-bottom-color: var(--orange);
    font-weight: 700;
  }
  .split {
    grid-template-columns: minmax(0, 4fr) minmax(0, 8fr);
    gap: 48px;
  }
  .split--reverse > :first-child { order: 0; }
  .toc__list {
    grid-template-columns: repeat(2, minmax(0, 1fr));
    column-gap: 40px;
  }
}

@media (min-width: 1000px) {
  .footer-grid {
    grid-template-columns: 1.5fr 1fr 1fr 1.4fr;
    gap: 40px;
  }
}