/* ==========================================================================
   BG品牌指南 · 全站共享样式 /assets/site.css
   深靛底 + 米白纸的黑白翻转节奏，信号橙为唯一强锚点
   ========================================================================== */

/* ---------- 设计令牌 ---------- */
:root{
  --ink:#0B1030;
  --ink-2:#141B47;
  --paper:#F5F2EA;
  --white:#FFFFFF;
  --signal:#FF5A1F;
  --signal-deep:#E04A12;
  --amber:#E8A33D;
  --mist:#CBD8DE;
  --slate:#6E7A99;
  --green:#2E9E7B;
  --text-dark:#2A2F45;
  --text-mute:#4A5570;

  --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",ui-monospace,SFMono-Regular,"SF Mono",Menlo,Consolas,"Liberation Mono",monospace;

  --shell-max:1320px;
  --line-dark:rgba(203,216,222,.18);
  --line-dark-strong:rgba(203,216,222,.34);
  --line-light:rgba(42,47,69,.14);

  --ease:cubic-bezier(.22,.68,.24,1);
  --shadow-soft:0 18px 44px -30px rgba(11,16,48,.75);
}

/* ---------- Reset ---------- */
*,*::before,*::after{box-sizing:border-box}
html{
  -webkit-text-size-adjust:100%;
  scroll-behavior:smooth;
  scroll-padding-top:124px;
}
body{
  margin:0;
  font-family:var(--font-sans);
  font-size:17px;
  line-height:1.85;
  color:var(--text-dark);
  background:var(--paper);
  -webkit-font-smoothing:antialiased;
  text-rendering:optimizeLegibility;
}
img,svg,video{display:block;max-width:100%;height:auto}
h1,h2,h3,h4,p,figure,blockquote,dl,dd,address{margin:0}
address{font-style:normal}
ul,ol{margin:0;padding:0;list-style:none}
a{color:inherit;text-decoration:none}
button{font:inherit;color:inherit;background:none;border:0}
table{border-collapse:collapse;width:100%}
:focus-visible{outline:2px solid var(--signal);outline-offset:3px}

/* ---------- 布局骨架 ---------- */
.shell{
  width:100%;
  max-width:var(--shell-max);
  margin-inline:auto;
  padding-inline:clamp(18px,4vw,44px);
}

.grid{display:grid;gap:clamp(18px,2.4vw,32px)}
.grid--2{grid-template-columns:repeat(2,minmax(0,1fr))}
.grid--3{grid-template-columns:repeat(3,minmax(0,1fr))}
.grid--4{grid-template-columns:repeat(4,minmax(0,1fr))}
.grid--aside{grid-template-columns:minmax(0,236px) minmax(0,1fr)}

.stack>*+*{margin-top:var(--stack-gap,18px)}
.cluster{display:flex;flex-wrap:wrap;align-items:center;gap:10px}

.divider{height:1px;border:0;margin:0;background:var(--line-dark)}
.divider--light{background:var(--line-light)}

/* ---------- 跳转链接 ---------- */
.skip-link{
  position:fixed;
  top:10px;
  left:10px;
  z-index:200;
  padding:10px 18px;
  background:var(--signal);
  color:#fff;
  font-size:14px;
  font-weight:700;
  letter-spacing:.05em;
  transform:translateY(-220%);
  transition:transform .2s var(--ease);
}
.skip-link:focus{transform:translateY(0)}

/* ---------- 页头 ---------- */
.masthead{
  position:sticky;
  top:0;
  z-index:90;
  color:var(--white);
  background:linear-gradient(180deg,rgba(11,16,48,.82) 0%,rgba(11,16,48,.34) 62%,rgba(11,16,48,0) 100%);
  transition:background-color .3s var(--ease),box-shadow .3s var(--ease);
}
.masthead.is-pinned{
  background:#0B1030;
  box-shadow:0 1px 0 var(--line-dark),0 16px 34px -28px rgba(0,0,0,.95);
}
.masthead__inner{
  display:flex;
  align-items:center;
  gap:clamp(14px,2vw,28px);
  padding-block:17px;
  transition:padding-block .28s var(--ease);
}
.masthead.is-pinned .masthead__inner{padding-block:8px}

/* 品牌 */
.brand{display:inline-flex;align-items:center;gap:12px;flex:0 0 auto}
.brand__mark{
  position:relative;
  display:grid;
  place-items:center;
  width:36px;
  height:36px;
  border:1px solid var(--line-dark-strong);
  font-family:var(--font-mono);
  font-size:12px;
  font-weight:700;
  letter-spacing:.04em;
  color:#fff;
}
.brand__mark::after{
  content:"";
  position:absolute;
  right:-1px;
  bottom:-1px;
  width:10px;
  height:10px;
  background:var(--signal);
}
.brand__text{display:flex;flex-direction:column;line-height:1.15}
.brand__name{font-size:17px;font-weight:800;letter-spacing:.06em}
.brand__tagline{font-size:11px;letter-spacing:.1em;color:rgba(203,216,222,.72)}

/* 工具组 */
.masthead__tools{
  margin-left:auto;
  display:flex;
  align-items:center;
  gap:10px;
}
.tool{
  display:inline-flex;
  align-items:center;
  gap:8px;
  padding:9px 15px;
  border:1px solid var(--line-dark-strong);
  font-size:13px;
  font-weight:600;
  letter-spacing:.06em;
  color:rgba(255,255,255,.84);
  white-space:nowrap;
  cursor:pointer;
  transition:color .2s var(--ease),border-color .2s var(--ease),background-color .2s var(--ease);
}
.tool:hover{color:#fff;border-color:rgba(203,216,222,.68);background:rgba(203,216,222,.09)}
.tool--ghost{border-style:dashed;color:rgba(203,216,222,.8)}
.tool[aria-pressed="true"]{
  border-style:solid;
  border-color:var(--signal);
  background:rgba(255,90,31,.16);
  color:#fff;
}

/* 移动端开关 */
.nav-toggle{
  display:none;
  align-items:center;
  gap:9px;
  padding:9px 14px;
  border:1px solid var(--line-dark-strong);
  color:#fff;
  font-size:13px;
  letter-spacing:.08em;
  cursor:pointer;
}
.nav-toggle__bars{
  position:relative;
  display:block;
  width:16px;
  height:1px;
  background:currentColor;
}
.nav-toggle__bars::before,
.nav-toggle__bars::after{
  content:"";
  position:absolute;
  left:0;
  width:16px;
  height:1px;
  background:currentColor;
  transition:transform .22s var(--ease),opacity .22s var(--ease);
}
.nav-toggle__bars::before{top:-5px}
.nav-toggle__bars::after{top:5px}
.nav-toggle[aria-expanded="true"] .nav-toggle__bars::before{transform:translateY(5px) rotate(45deg)}
.nav-toggle[aria-expanded="true"] .nav-toggle__bars::after{transform:translateY(-5px) rotate(-45deg)}
.nav-toggle[aria-expanded="true"] .nav-toggle__bars{background:transparent}

/* 栏目索引条 */
.nav{border-top:1px solid var(--line-dark)}
.nav__list{
  width:100%;
  max-width:var(--shell-max);
  margin-inline:auto;
  padding-inline:clamp(18px,4vw,44px);
  display:flex;
  align-items:center;
  gap:clamp(10px,2.6vw,36px);
}
.nav__item{flex:0 0 auto}
.nav__link{
  position:relative;
  display:block;
  padding:12px 2px;
  font-size:14px;
  letter-spacing:.05em;
  color:rgba(255,255,255,.74);
  transition:color .2s var(--ease);
}
.nav__link::after{
  content:"";
  position:absolute;
  left:0;
  bottom:7px;
  width:0;
  height:2px;
  background:var(--signal);
  transition:width .26s var(--ease);
}
.nav__link:hover{color:#fff}
.nav__link:hover::after{width:100%}
.nav__link[aria-current="page"]{color:#fff;font-weight:700}
.nav__link[aria-current="page"]::after{width:100%}

/* ---------- 页脚 ---------- */
.site-footer{
  position:relative;
  background:var(--ink);
  color:#fff;
}
.site-footer__edge{
  height:32px;
  background:
    repeating-linear-gradient(90deg,rgba(203,216,222,.26) 0 1px,transparent 1px 32px),
    linear-gradient(180deg,rgba(11,16,48,0) 0%,rgba(20,27,71,.85) 100%);
  border-bottom:1px solid var(--line-dark);
  position:relative;
}
.site-footer__edge::after{
  content:"";
  position:absolute;
  left:0;
  bottom:-1px;
  width:min(240px,38%);
  height:2px;
  background:var(--signal);
}
.site-footer__inner{
  display:grid;
  grid-template-columns:minmax(0,1fr) minmax(0,1.65fr);
  gap:clamp(26px,4vw,64px);
  padding-block:clamp(38px,5.4vw,68px) clamp(26px,3.6vw,40px);
}
.site-footer__name{font-size:22px;font-weight:800;letter-spacing:.08em}
.site-footer__tagline{
  margin-top:8px;
  font-size:12px;
  letter-spacing:.14em;
  color:var(--amber);
}
.site-footer__note{
  margin-top:18px;
  max-width:42ch;
  font-size:14px;
  line-height:1.9;
  color:rgba(203,216,222,.72);
}
.site-footer__cols{
  display:grid;
  grid-template-columns:repeat(4,minmax(0,1fr));
  gap:clamp(16px,2vw,32px);
}
.site-footer__title{
  font-size:12px;
  font-weight:700;
  letter-spacing:.16em;
  color:var(--mist);
  padding-bottom:12px;
  border-bottom:1px solid var(--line-dark);
}
.site-footer__links{margin-top:14px;display:grid;gap:10px}
.site-footer__links a{
  font-size:14px;
  color:rgba(255,255,255,.76);
  transition:color .2s var(--ease),padding-left .2s var(--ease);
}
.site-footer__links a:hover{color:var(--signal);padding-left:4px}
.site-footer__contact{padding-block:0 clamp(20px,2.6vw,28px)}
.site-footer__address{
  display:flex;
  flex-wrap:wrap;
  gap:8px 14px;
  padding-top:22px;
  border-top:1px solid var(--line-dark);
  font-family:var(--font-mono);
  font-size:13px;
  letter-spacing:.02em;
  color:rgba(203,216,222,.86);
}
.site-footer__legal{
  display:flex;
  flex-wrap:wrap;
  align-items:center;
  justify-content:space-between;
  gap:12px 24px;
  padding-block:0 clamp(28px,3.4vw,44px);
}
.site-footer__copy{font-size:12px;letter-spacing:.06em;color:rgba(203,216,222,.6)}
.site-footer__legal-links{display:flex;flex-wrap:wrap;gap:8px 20px}
.site-footer__legal-links a{
  font-size:12px;
  letter-spacing:.06em;
  color:rgba(203,216,222,.7);
}
.site-footer__legal-links a:hover{color:var(--signal)}

/* ---------- 通用按钮 ---------- */
.btn{
  display:inline-flex;
  align-items:center;
  justify-content:center;
  gap:9px;
  padding:13px 22px;
  border:1px solid transparent;
  font-size:14px;
  font-weight:700;
  letter-spacing:.06em;
  cursor:pointer;
  transition:background-color .2s var(--ease),color .2s var(--ease),border-color .2s var(--ease),transform .2s var(--ease);
}
.btn:hover{transform:translateY(-1px)}
.btn:active{transform:translateY(0)}
.btn--sm{padding:10px 16px;font-size:13px}
.btn--signal{background:var(--signal);color:#fff}
.btn--signal:hover{background:var(--signal-deep)}
.btn--line{border-color:currentColor;color:inherit}
.btn--line:hover{background:rgba(255,90,31,.12);border-color:var(--signal);color:var(--signal)}
.btn--ghost{border-color:var(--line-dark-strong);color:inherit}
.btn--ghost:hover{border-color:var(--signal);color:var(--signal)}

/* ---------- 面包屑 ---------- */
.crumbs{
  display:flex;
  flex-wrap:wrap;
  gap:6px 10px;
  font-family:var(--font-mono);
  font-size:12px;
  letter-spacing:.08em;
  color:var(--slate);
}
.crumbs li{display:flex;align-items:center;gap:10px}
.crumbs li+li::before{content:"/";opacity:.55}
.crumbs a{color:inherit;transition:color .2s var(--ease)}
.crumbs a:hover{color:var(--signal)}
.crumbs [aria-current="page"]{color:currentColor;font-weight:700}

/* ---------- 章节小标 ---------- */
.eyebrow{
  display:inline-flex;
  align-items:center;
  gap:10px;
  font-family:var(--font-mono);
  font-size:12px;
  font-weight:600;
  letter-spacing:.2em;
  text-transform:uppercase;
  color:var(--amber);
}
.eyebrow::before{
  content:"";
  width:26px;
  height:2px;
  background:var(--signal);
}

/* ---------- 正文容器 ---------- */
.prose{max-width:64ch;font-size:17px;line-height:1.85}
.prose p+p{margin-top:1em}
.prose ul,.prose ol{margin-top:1em;padding-left:1.2em;list-style:disc}
.prose li+li{margin-top:.4em}
.prose a{color:var(--signal);text-decoration:underline;text-underline-offset:3px}

/* ---------- 标签 ---------- */
.tag{
  display:inline-flex;
  align-items:center;
  gap:6px;
  padding:5px 10px;
  border:1px solid currentColor;
  font-family:var(--font-mono);
  font-size:11px;
  font-weight:600;
  letter-spacing:.12em;
  text-transform:uppercase;
  white-space:nowrap;
}
.tag--signal{color:var(--signal)}
.tag--amber{color:var(--amber)}
.tag--mist{color:var(--slate)}
.tag--green{color:var(--green)}

/* ---------- 数字 ---------- */
.mono{font-family:var(--font-mono);font-variant-numeric:tabular-nums}
.stat{
  padding:22px 22px 20px;
  background:rgba(20,27,71,.62);
  border:1px solid var(--line-dark);
  box-shadow:var(--shadow-soft);
}
.stat__value{
  display:block;
  font-family:var(--font-mono);
  font-size:clamp(40px,5vw,60px);
  font-weight:700;
  line-height:1;
  letter-spacing:-.02em;
  color:var(--amber);
}
.stat__label{
  margin-top:12px;
  font-size:13px;
  letter-spacing:.08em;
  color:rgba(255,255,255,.74);
}

/* ---------- 多语言对照行 ---------- */
.langpair{
  display:grid;
  grid-template-columns:56px minmax(0,1fr);
  gap:16px;
  padding:14px 18px;
  border-bottom:1px solid rgba(110,122,153,.22);
}
.langpair:nth-child(odd){background:rgba(203,216,222,.2)}
.langpair__tag{
  font-family:var(--font-mono);
  font-size:12px;
  font-weight:600;
  letter-spacing:.14em;
  line-height:1.95;
  text-transform:uppercase;
  color:var(--slate);
}
.langpair__cn{font-weight:600;color:var(--text-dark)}
.langpair__alt{font-size:15px;line-height:1.95;color:var(--text-mute)}

/* ---------- 整宽色带 ---------- */
.band{padding-block:clamp(56px,7.6vw,110px)}
.band--ink{background:var(--ink);color:#fff}
.band--ink-2{background:var(--ink-2);color:#fff}
.band--paper{background:var(--paper);color:var(--text-dark)}
.band--mist{background:var(--mist);color:var(--text-dark)}
.band--ink .eyebrow,.band--ink-2 .eyebrow{color:var(--amber)}

/* ---------- 图片容器（页面阶段放置图片） ---------- */
.figure{
  position:relative;
  margin:0;
  overflow:hidden;
  background:var(--ink-2);
}
.figure--framed{border:1px solid rgba(110,122,153,.35)}
.figure__media{
  display:block;
  width:100%;
  aspect-ratio:16/9;
  object-fit:cover;
}
.figure--portrait .figure__media{aspect-ratio:4/5}
.figure--wide .figure__media{aspect-ratio:21/9}
.figure--square .figure__media{aspect-ratio:1/1}
.figure-caption{
  display:block;
  margin-top:10px;
  font-size:13px;
  line-height:1.75;
  letter-spacing:.02em;
  color:var(--slate);
}

/* ---------- 显现动效 ---------- */
.js-on [data-reveal]{
  opacity:0;
  transform:translateY(22px);
  transition:opacity .7s var(--ease),transform .7s var(--ease);
}
.js-on [data-reveal].is-in{opacity:1;transform:none}

/* ---------- 手机版预览 ---------- */
html[data-view="compact"] main .shell{
  max-width:440px;
  outline:1px dashed rgba(110,122,153,.5);
  outline-offset:16px;
}

/* ---------- 响应式 ---------- */
@media (max-width:1180px){
  .grid--aside{grid-template-columns:minmax(0,200px) minmax(0,1fr)}
}

@media (max-width:1080px){
  .nav-toggle{display:inline-flex}
  .nav{
    position:absolute;
    left:0;
    right:0;
    top:100%;
    max-height:0;
    overflow:hidden;
    background:var(--ink-2);
    border-top:1px solid var(--line-dark);
    border-bottom:1px solid var(--line-dark);
    transition:max-height .34s var(--ease);
  }
  .nav[data-open]{max-height:min(74vh,560px);overflow-y:auto}
  .nav__list{
    flex-direction:column;
    align-items:stretch;
    gap:0;
    padding-block:6px 20px;
  }
  .nav__link{
    padding:15px 0;
    font-size:15px;
    border-bottom:1px solid var(--line-dark);
  }
  .nav__link::after{display:none}
  .nav__link[aria-current="page"]{color:var(--signal)}
}

@media (max-width:960px){
  .site-footer__inner{grid-template-columns:minmax(0,1fr)}
  .site-footer__cols{grid-template-columns:repeat(2,minmax(0,1fr))}
  .grid--3,.grid--4{grid-template-columns:repeat(2,minmax(0,1fr))}
  .grid--aside{grid-template-columns:minmax(0,1fr)}
}

@media (max-width:760px){
  body{font-size:16px;line-height:1.8}
  html{scroll-padding-top:104px}
  .masthead__tools{gap:8px}
  .masthead__tools .tool:not(.tool--ghost){display:none}
  .masthead__tools .btn--sm{display:none}
  .brand__tagline{display:none}
  .grid--2,.grid--3,.grid--4{grid-template-columns:minmax(0,1fr)}
  .site-footer__cols{grid-template-columns:minmax(0,1fr);gap:24px}
  .langpair{grid-template-columns:44px minmax(0,1fr);gap:12px;padding:13px 14px}
  .site-footer__legal{flex-direction:column;align-items:flex-start}
}

/* ---------- 动效偏好 ---------- */
@media (prefers-reduced-motion:reduce){
  html{scroll-behavior:auto}
  *,*::before,*::after{
    animation-duration:.001ms !important;
    animation-iteration-count:1 !important;
    transition-duration:.001ms !important;
  }
  .js-on [data-reveal]{opacity:1;transform:none}
  .skip-link{transition:none}
}