/* ==========================================================================
   北单CN中国站 · 共享样式表 /assets/site.css
   结构：1 Reset · 2 Tokens · 3 Base · 4 Header · 5 Nav Drawer · 6 Rail
        7 Footer · 8 Components · 9 Motion · 10 Responsive
   ========================================================================== */

/* 1. Reset ---------------------------------------------------------------- */
*, *::before, *::after { box-sizing: border-box; }
html { -webkit-text-size-adjust: 100%; scroll-behavior: smooth; }
body { margin: 0; }
img, svg, picture, video, canvas { display: block; max-width: 100%; }
button, input, select, textarea { font: inherit; color: inherit; }
ul, ol { margin: 0; padding: 0; list-style: none; }
h1, h2, h3, h4, h5, h6, p, figure, blockquote, dl, dd { margin: 0; }
a { color: inherit; text-decoration: none; }
table { border-collapse: collapse; width: 100%; }

/* 2. Tokens --------------------------------------------------------------- */
:root {
  --c-blue: #0A2A5E;
  --c-blue-2: #123D7A;
  --c-orange: #FF6B35;
  --c-orange-soft: #FFA07A;
  --c-cream: #F7F3EA;
  --c-gray: #E9ECEF;
  --c-ink: #1F1F1F;
  --c-line: #C9BFAF;
  --c-body: #3F4A61;
  --c-ok: #2F8F5B;
  --c-warn: #D97706;
  --c-alert: #B42318;

  --font-sans: "Inter", "Helvetica Neue", Arial, "PingFang SC", "Microsoft YaHei", "Source Han Sans SC", "Noto Sans SC", sans-serif;
  --font-mono: "IBM Plex Mono", ui-monospace, "SFMono-Regular", Menlo, Consolas, monospace;

  --wrap: 1200px;
  --gutter: clamp(18px, 4vw, 56px);
  --bw: 3px;
  --shadow-hard: 7px 7px 0 rgba(10, 42, 94, .16);
  --ease: cubic-bezier(.22, .61, .36, 1);
}

/* 3. Base ----------------------------------------------------------------- */
html { background: var(--c-cream); }
body {
  font-family: var(--font-sans);
  font-weight: 500;
  font-size: clamp(15px, .35vw + 14px, 17px);
  line-height: 1.75;
  letter-spacing: .01em;
  color: var(--c-ink);
  background: var(--c-cream);
  overflow-x: hidden;
}
body[data-nav-open="true"] { overflow: hidden; }

h1, h2, h3, h4 { font-weight: 900; line-height: 1.18; letter-spacing: -.02em; color: var(--c-blue); }
strong { font-weight: 800; }

.wrap {
  width: 100%;
  max-width: var(--wrap);
  margin-inline: auto;
  padding-inline: var(--gutter);
}

#main-content { scroll-margin-top: 130px; }

:focus-visible { outline: 3px solid var(--c-orange); outline-offset: 3px; }

.skip-link {
  position: absolute;
  left: -9999px;
  top: 0;
  z-index: 200;
  padding: 12px 22px;
  background: var(--c-orange);
  color: var(--c-blue);
  font-weight: 800;
  font-size: 14px;
  border: var(--bw) solid var(--c-blue);
}
.skip-link:focus { left: var(--gutter); top: 10px; }

/* 4. Header --------------------------------------------------------------- */
.site-header {
  position: sticky;
  top: 0;
  z-index: 80;
  background: var(--c-cream);
  transition: box-shadow .25s var(--ease);
}
.site-header[data-scrolled="true"] { box-shadow: 0 10px 0 rgba(10, 42, 94, .1); }

.header-strip {
  background: var(--c-gray);
  color: var(--c-blue);
  border-bottom: 2px solid var(--c-line);
  font-family: var(--font-mono);
  font-size: 11px;
  letter-spacing: .14em;
  text-transform: uppercase;
}
.header-strip__inner {
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  justify-content: space-between;
  gap: 6px 20px;
  min-height: 36px;
  padding-block: 6px;
}
.strip-tag { font-weight: 700; color: var(--c-blue); white-space: nowrap; }
.strip-tag::before {
  content: "";
  display: inline-block;
  width: 8px; height: 8px;
  margin-right: 8px;
  background: var(--c-orange);
  vertical-align: 1px;
}
.strip-meta { color: #4A5568; white-space: nowrap; }

.header-bar { position: relative; background: var(--c-blue); color: #fff; }
.header-bar__inner {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 20px;
  min-height: 76px;
  padding-block: 12px;
}

/* brand */
.brand { display: inline-flex; align-items: center; gap: 12px; color: #fff; }
.brand__mark {
  display: grid;
  place-items: center;
  width: 44px; height: 44px;
  flex: none;
  background: var(--c-orange);
  color: var(--c-blue);
  font-weight: 900;
  font-size: 16px;
  letter-spacing: -.03em;
}
.brand__text { display: flex; flex-direction: column; }
.brand__name {
  display: block;
  font-size: clamp(17px, 1.1vw + 13px, 21px);
  font-weight: 900;
  line-height: 1.2;
  letter-spacing: .01em;
  color: #fff;
}
.brand__meta {
  display: block;
  font-family: var(--font-mono);
  font-size: 10px;
  letter-spacing: .18em;
  text-transform: uppercase;
  color: var(--c-orange-soft);
}

/* nav list base (mobile drawer) */
.primary-nav {
  position: fixed;
  top: 0; right: 0; bottom: 0;
  z-index: 70;
  width: min(86vw, 360px);
  display: flex;
  flex-direction: column;
  padding: 140px 26px 44px;
  background: var(--c-blue);
  border-left: var(--bw) solid var(--c-orange);
  overflow-y: auto;
  overscroll-behavior: contain;
  transform: translateX(103%);
  transition: transform .38s var(--ease);
}
.primary-nav[data-open] { transform: translateX(0); }

.nav-list { display: flex; flex-direction: column; width: 100%; }
.nav-list__item { border-bottom: 2px solid rgba(255, 255, 255, .12); }
.nav-list__item:last-child { border-bottom: 0; }
.nav-list--end {
  margin-top: 24px;
  padding-top: 24px;
  border-top: 2px dashed rgba(255, 255, 255, .26);
}

.nav-link {
  position: relative;
  display: block;
  padding: 16px 4px;
  font-size: 17px;
  font-weight: 700;
  letter-spacing: .02em;
  color: #fff;
  white-space: nowrap;
  transition: color .2s var(--ease);
}
.nav-link::after {
  content: "";
  position: absolute;
  left: 0; right: 100%;
  bottom: 6px;
  height: 3px;
  background: var(--c-orange);
  transition: right .28s var(--ease);
}
.nav-link:hover { color: var(--c-orange-soft); }
.nav-link[aria-current="page"] { color: var(--c-orange); }

.nav-list__item--cta { margin-top: 20px; border-bottom: 0; }
.nav-list__item--cta .btn { width: 100%; }

/* toggle */
.nav-toggle {
  display: inline-flex;
  align-items: center;
  gap: 10px;
  padding: 10px 14px;
  background: transparent;
  border: 2px solid rgba(255, 255, 255, .5);
  color: #fff;
  font-size: 13px;
  font-weight: 800;
  letter-spacing: .12em;
  cursor: pointer;
  transition: border-color .2s var(--ease), color .2s var(--ease);
}
.nav-toggle:hover { border-color: var(--c-orange); color: var(--c-orange); }
.nav-toggle__bars {
  position: relative;
  display: block;
  width: 20px; height: 2px;
  background: currentColor;
  transition: background-color .2s var(--ease);
}
.nav-toggle__bars::before,
.nav-toggle__bars::after {
  content: "";
  position: absolute;
  left: 0;
  width: 20px; height: 2px;
  background: currentColor;
  transition: transform .24s var(--ease);
}
.nav-toggle__bars::before { top: -6px; }
.nav-toggle__bars::after { top: 6px; }
.nav-toggle[aria-expanded="true"] .nav-toggle__bars { background: transparent; }
.nav-toggle[aria-expanded="true"] .nav-toggle__bars::before { transform: translateY(6px) rotate(45deg); }
.nav-toggle[aria-expanded="true"] .nav-toggle__bars::after { transform: translateY(-6px) rotate(-45deg); }

/* scroll progress */
.scroll-progress {
  position: absolute;
  left: 0; right: 0; bottom: 0;
  height: 4px;
  background: rgba(255, 255, 255, .16);
  overflow: hidden;
}
.scroll-progress__bar {
  display: block;
  width: 100%; height: 100%;
  background: var(--c-orange);
  transform: scaleX(0);
  transform-origin: left center;
  transition: transform .1s linear;
}

/* 5. Desktop navigation layout -------------------------------------------- */
@media (min-width: 920px) {
  .header-bar__inner {
    display: grid;
    grid-template-columns: minmax(0, 1fr) auto minmax(0, 1fr);
    align-items: center;
    gap: 24px;
    min-height: 88px;
  }
  .primary-nav {
    display: contents;
    position: static;
    width: auto;
    padding: 0;
    background: transparent;
    border: 0;
    transform: none;
    overflow: visible;
  }
  .nav-list { flex-direction: row; align-items: center; width: auto; gap: clamp(12px, 1.6vw, 28px); }
  .nav-list--start { grid-column: 1; justify-self: start; }
  .nav-list--end { grid-column: 3; justify-self: end; margin-top: 0; padding-top: 0; border-top: 0; }
  .nav-list__item { border-bottom: 0; }
  .nav-list__item--cta { margin-top: 0; }
  .nav-list__item--cta .btn { width: auto; }
  .nav-link { display: inline-block; padding: 10px 2px; font-size: 14.5px; }
  .nav-link::after { bottom: 4px; }
  .nav-link:hover::after { right: 0; }
  .nav-link[aria-current="page"]::after { right: 0; }
  .brand { grid-column: 2; justify-self: center; }
  .nav-toggle { display: none; }
}

/* 6. Coord rail ----------------------------------------------------------- */
.coord-rail { display: none; }
@media (min-width: 1380px) {
  .coord-rail {
    display: flex;
    flex-direction: column;
    align-items: center;
    gap: 14px;
    position: fixed;
    right: 0;
    top: 50%;
    transform: translateY(-50%);
    z-index: 60;
    padding: 20px 10px;
    background: var(--c-blue);
    border-left: var(--bw) solid var(--c-orange);
    box-shadow: -6px 0 0 rgba(10, 42, 94, .1);
  }
  .coord-rail__title {
    writing-mode: vertical-rl;
    font-family: var(--font-mono);
    font-size: 10px;
    letter-spacing: .32em;
    text-transform: uppercase;
    color: var(--c-orange-soft);
  }
  .coord-rail__list { display: flex; flex-direction: column; align-items: center; gap: 4px; }
  .coord-rail__item { border-top: 1px solid rgba(255, 255, 255, .18); }
  .coord-rail__item:first-child { border-top: 0; }
  .coord-link {
    display: flex;
    flex-direction: column;
    align-items: center;
    gap: 8px;
    padding: 12px 8px;
    color: #fff;
    transition: background-color .2s var(--ease), color .2s var(--ease);
  }
  .coord-link:hover { background: var(--c-orange); color: var(--c-blue); }
  .coord-link:hover .coord-link__num { color: var(--c-blue); }
  .coord-link[aria-current="page"] { background: var(--c-orange); color: var(--c-blue); }
  .coord-link[aria-current="page"] .coord-link__num { color: var(--c-blue); }
  .coord-link__num {
    font-family: var(--font-mono);
    font-size: 10px;
    letter-spacing: .1em;
    color: var(--c-orange);
  }
  .coord-link__text {
    writing-mode: vertical-rl;
    font-size: 12px;
    font-weight: 700;
    letter-spacing: .2em;
  }
}

/* 7. Footer --------------------------------------------------------------- */
.site-footer {
  background: var(--c-blue);
  color: #fff;
  border-top: 6px solid var(--c-orange);
  font-size: 15px;
}
.footer-grid {
  display: grid;
  grid-template-columns: 1fr;
  gap: clamp(28px, 4vw, 56px);
  padding-block: clamp(48px, 6vw, 84px);
}
.footer-logo {
  display: inline-block;
  font-size: clamp(22px, 2vw + 12px, 30px);
  font-weight: 900;
  letter-spacing: -.01em;
  color: #fff;
}
.footer-tagline {
  margin-top: 12px;
  font-family: var(--font-mono);
  font-size: 12px;
  letter-spacing: .22em;
  text-transform: uppercase;
  color: var(--c-orange);
}
.footer-desc {
  margin-top: 16px;
  max-width: 34em;
  font-size: 14.5px;
  line-height: 1.8;
  color: rgba(255, 255, 255, .72);
}
.footer-col__title {
  margin-bottom: 18px;
  font-size: 13px;
  font-weight: 800;
  letter-spacing: .2em;
  color: var(--c-orange);
}
.footer-links { display: flex; flex-direction: column; gap: 10px; }
.footer-link {
  display: inline-block;
  font-size: 14.5px;
  color: rgba(255, 255, 255, .8);
  border-bottom: 2px solid transparent;
  transition: color .2s var(--ease), border-color .2s var(--ease);
}
.footer-link:hover { color: var(--c-orange); border-bottom-color: var(--c-orange); }
.footer-link[aria-current="page"] { color: var(--c-orange); border-bottom-color: var(--c-orange); }

.contact-list { display: flex; flex-direction: column; gap: 14px; }
.contact-line {
  display: grid;
  grid-template-columns: 54px minmax(0, 1fr);
  gap: 12px;
  padding-bottom: 12px;
  border-bottom: 1px dashed rgba(255, 255, 255, .2);
}
.contact-line:last-child { border-bottom: 0; padding-bottom: 0; }
.contact-line__label {
  font-family: var(--font-mono);
  font-size: 11px;
  letter-spacing: .16em;
  color: var(--c-orange-soft);
  text-transform: uppercase;
}
.contact-line__value { font-size: 14.5px; color: #fff; word-break: break-word; }

.footer-note {
  padding-block: 22px;
  border-top: 1px dashed rgba(255, 255, 255, .22);
  font-size: 13px;
  color: rgba(255, 255, 255, .68);
}
.footer-note p { max-width: 68em; }
.link-inline {
  color: var(--c-orange);
  border-bottom: 2px solid rgba(255, 107, 53, .5);
  transition: border-color .2s var(--ease);
}
.link-inline:hover { border-bottom-color: var(--c-orange); }

.footer-meta {
  background: rgba(0, 0, 0, .24);
  border-top: 1px solid rgba(255, 255, 255, .14);
}
.footer-meta__inner {
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  justify-content: space-between;
  gap: 10px 26px;
  padding-block: 20px;
  font-size: 12.5px;
  color: rgba(255, 255, 255, .68);
}
.footer-copy { font-family: var(--font-mono); letter-spacing: .06em; }
.footer-legal { display: inline-flex; align-items: center; gap: 10px; flex-wrap: wrap; }
.footer-legal .footer-link { font-size: 12.5px; }
.footer-sep { color: rgba(255, 255, 255, .34); }
.footer-icp { font-family: var(--font-mono); letter-spacing: .06em; }

/* 8. Reusable components -------------------------------------------------- */
.btn {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  gap: 8px;
  padding: 12px 22px;
  background: var(--c-cream);
  border: var(--bw) solid var(--c-blue);
  color: var(--c-blue);
  font-size: 14px;
  font-weight: 800;
  letter-spacing: .02em;
  text-align: center;
  cursor: pointer;
  transition: transform .18s var(--ease), box-shadow .18s var(--ease),
              background-color .18s var(--ease), color .18s var(--ease),
              border-color .18s var(--ease);
}
.btn:hover { transform: translate(-2px, -2px); }
.btn--primary {
  background: var(--c-orange);
  border-color: var(--c-orange);
  color: #08203F;
  box-shadow: 4px 4px 0 rgba(255, 255, 255, .22);
}
.btn--primary:hover { box-shadow: 7px 7px 0 rgba(255, 255, 255, .3); }
.btn--ghost {
  background: transparent;
  border-color: currentColor;
  color: inherit;
}
.btn--ghost:hover { background: var(--c-orange); border-color: var(--c-orange); color: #08203F; }
.btn--line { box-shadow: 5px 5px 0 var(--c-blue); }
.btn--line:hover { box-shadow: 8px 8px 0 var(--c-blue); }
.btn--sm { padding: 8px 14px; font-size: 13px; }

.section { padding-block: clamp(56px, 7vw, 110px); }
.section--tight { padding-block: clamp(36px, 4vw, 64px); }
.section--blue { background: var(--c-blue); color: #fff; }
.section--blue h1, .section--blue h2, .section--blue h3 { color: #fff; }
.section--gray { background: var(--c-gray); }

.section-head { max-width: 64ch; margin-bottom: clamp(28px, 3.5vw, 52px); }
.eyebrow {
  display: inline-flex;
  align-items: center;
  gap: 10px;
  margin-bottom: 14px;
  font-family: var(--font-mono);
  font-size: 11px;
  letter-spacing: .26em;
  text-transform: uppercase;
  color: var(--c-orange);
}
.eyebrow::before {
  content: "";
  width: 22px; height: 3px;
  background: var(--c-orange);
}
.section-title { font-size: clamp(28px, 3.6vw, 52px); }
.section-lead { margin-top: 16px; max-width: 56ch; font-size: clamp(15px, .5vw + 14px, 17px); color: var(--c-body); }
.section--blue .section-lead { color: rgba(255, 255, 255, .76); }

.grid { display: grid; gap: clamp(18px, 2.4vw, 32px); grid-template-columns: 1fr; }
@media (min-width: 640px) {
  .grid--2, .grid--3, .grid--4 { grid-template-columns: repeat(2, minmax(0, 1fr)); }
}
@media (min-width: 980px) {
  .grid--3 { grid-template-columns: repeat(3, minmax(0, 1fr)); }
  .grid--4 { grid-template-columns: repeat(4, minmax(0, 1fr)); }
}

.card {
  position: relative;
  padding: clamp(20px, 2.2vw, 30px);
  background: #fff;
  border: var(--bw) solid var(--c-blue);
  box-shadow: var(--shadow-hard);
  transition: transform .2s var(--ease), box-shadow .2s var(--ease);
}
.card:hover { transform: translate(-3px, -3px); box-shadow: 10px 10px 0 rgba(10, 42, 94, .2); }
.card__meta {
  display: block;
  margin-bottom: 12px;
  font-family: var(--font-mono);
  font-size: 11px;
  letter-spacing: .16em;
  text-transform: uppercase;
  color: var(--c-orange);
}
.card__title { margin-bottom: 10px; font-size: 20px; }
.card__text { font-size: 15px; line-height: 1.75; color: var(--c-body); }
.card--blue { background: var(--c-blue-2); border-color: var(--c-blue); color: #fff; }
.card--blue .card__title { color: #fff; }
.card--blue .card__text { color: rgba(255, 255, 255, .78); }

.stat { display: flex; flex-direction: column; gap: 6px; }
.stat__value {
  font-family: var(--font-mono);
  font-weight: 700;
  font-size: clamp(30px, 4.4vw, 56px);
  line-height: 1.02;
  letter-spacing: -.02em;
  color: var(--c-orange);
}
.stat__unit { margin-left: 6px; font-family: var(--font-sans); font-size: 14px; font-weight: 700; color: var(--c-body); }
.stat__label { font-size: 13px; letter-spacing: .1em; color: #5A6580; }
.section--blue .stat__label { color: rgba(255, 255, 255, .72); }
.section--blue .stat__unit { color: rgba(255, 255, 255, .8); }

.tag {
  display: inline-flex;
  align-items: center;
  gap: 6px;
  padding: 4px 10px;
  border: 2px solid currentColor;
  background: transparent;
  font-size: 12px;
  font-weight: 700;
  letter-spacing: .04em;
}
.tag--ok { color: var(--c-ok); }
.tag--warn { color: var(--c-warn); }
.tag--alert { color: var(--c-alert); }
.tag--orange { color: var(--c-orange); }
.tag--solid { background: var(--c-orange); border-color: var(--c-orange); color: #08203F; }

.meter { display: flex; flex-direction: column; gap: 8px; }
.meter__track {
  height: 14px;
  background: var(--c-gray);
  border: 2px solid var(--c-blue);
  overflow: hidden;
}
.meter__fill {
  display: block;
  width: var(--meter, 60%);
  height: 100%;
  background: var(--c-orange);
  transition: width .8s var(--ease);
}
.section--blue .meter__track { background: rgba(255, 255, 255, .14); border-color: rgba(255, 255, 255, .4); }

.figure {
  margin: 0;
  border: var(--bw) solid var(--c-blue);
  background: var(--c-gray);
  box-shadow: var(--shadow-hard);
  overflow: hidden;
}
.figure__media {
  position: relative;
  width: 100%;
  aspect-ratio: 16 / 10;
  display: grid;
  place-items: center;
  background-color: var(--c-gray);
  background-image:
    radial-gradient(rgba(10, 42, 94, .2) 1.2px, transparent 1.3px),
    linear-gradient(180deg, rgba(10, 42, 94, .05), rgba(10, 42, 94, 0));
  background-size: 14px 14px, 100% 100%;
  overflow: hidden;
}
.figure__media > img,
.figure__media > svg {
  position: absolute;
  inset: 0;
  width: 100%;
  height: 100%;
  object-fit: cover;
}
.figure--wide .figure__media { aspect-ratio: 21 / 9; }
.figure--tall .figure__media { aspect-ratio: 4 / 5; }
.figure--square .figure__media { aspect-ratio: 1 / 1; }
.figure__cap {
  display: flex;
  flex-wrap: wrap;
  justify-content: space-between;
  gap: 8px 16px;
  padding: 12px 16px;
  background: var(--c-blue);
  color: #fff;
  font-family: var(--font-mono);
  font-size: 12px;
  letter-spacing: .06em;
}

.prose { max-width: 72ch; color: var(--c-ink); }
.prose h2 { margin: 2em 0 .6em; font-size: clamp(22px, 2.4vw, 32px); }
.prose h3 { margin: 1.6em 0 .5em; font-size: clamp(18px, 1.6vw, 22px); }
.prose p { margin: 0 0 1.1em; }
.prose ul, .prose ol { margin: 0 0 1.2em; padding-left: 1.4em; list-style: disc; }
.prose ol { list-style: decimal; }
.prose li { margin-bottom: .5em; }
.prose a { color: var(--c-blue); text-decoration: underline; text-decoration-thickness: 2px; text-underline-offset: 3px; }
.prose a:hover { color: var(--c-orange); }
.prose strong { color: var(--c-blue); }

.note {
  padding: 16px 20px;
  background: var(--c-gray);
  border-left: 6px solid var(--c-orange);
  font-size: 14.5px;
  color: var(--c-body);
}

.breadcrumb { background: var(--c-cream); border-bottom: 2px solid var(--c-line); }
.breadcrumb__list {
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  gap: 10px;
  padding-block: 18px;
  font-family: var(--font-mono);
  font-size: 12px;
  letter-spacing: .08em;
  color: #5A6580;
}
.breadcrumb__item { display: flex; align-items: center; gap: 10px; }
.breadcrumb__item[aria-current="page"] { color: var(--c-ink); font-weight: 700; }
.breadcrumb__link { color: var(--c-blue); border-bottom: 2px solid transparent; }
.breadcrumb__link:hover { color: var(--c-orange); border-bottom-color: var(--c-orange); }
.breadcrumb__sep { color: var(--c-line); }

/* 9. Motion --------------------------------------------------------------- */
[data-reveal] {
  opacity: 0;
  transform: translateY(20px);
  transition: opacity .7s var(--ease), transform .7s var(--ease);
  transition-delay: var(--reveal-delay, 0s);
}
[data-reveal].is-in { opacity: 1; transform: none; }

@media (prefers-reduced-motion: reduce) {
  html { scroll-behavior: auto; }
  *, *::before, *::after {
    animation-duration: .01ms !important;
    animation-iteration-count: 1 !important;
    transition-duration: .01ms !important;
  }
  [data-reveal] { opacity: 1; transform: none; }
  .primary-nav { transition: none; }
  .scroll-progress__bar { transition: none; }
}

/* 10. Responsive ---------------------------------------------------------- */
@media (max-width: 560px) {
  .strip-meta--hide-sm { display: none; }
  .header-strip { font-size: 10px; letter-spacing: .1em; }
  .header-bar__inner { min-height: 68px; }
  .brand__meta { display: none; }
  .primary-nav { padding-top: 124px; }
  .footer-meta__inner { font-size: 12px; }
}
@media (max-width: 380px) {
  .nav-toggle__label { display: none; }
}