/* ===== 北单主页 · 共享样式表 /assets/site.css ===== */

:root{
  --ink-900:#0A1A2F;
  --ink-800:#10243D;
  --ink-700:#16324F;
  --line:#2A3F55;
  --text:#E8F1F8;
  --text-mute:#9FB6CC;
  --cyan:#00E5C8;
  --amber:#FFB347;
  --coral:#FF6B4A;
  --cyan-hover:#4DD0E1;

  --shell:min(1280px, calc(100% - 48px));
  --ease:120ms cubic-bezier(.4,0,.2,1);
  --sans:"Source Han Sans SC","Noto Sans SC","PingFang SC","Hiragino Sans GB","Microsoft YaHei",system-ui,sans-serif;
  --mono:"IBM Plex Mono","SFMono-Regular",Consolas,"Liberation Mono",monospace;

  --t-label:12px;
  --t-xs:13px;
  --t-sm:15px;
  --t-md:16px;
  --t-lg:20px;
  --t-xl:28px;
  --t-2xl:40px;
  --t-3xl:56px;
}

/* ----- reset ----- */
*,*::before,*::after{box-sizing:border-box}
html{background-color:var(--ink-900);scroll-behavior:smooth;-webkit-text-size-adjust:100%}
body{
  margin:0;
  background-color:transparent;
  color:var(--text);
  font-family:var(--sans);
  font-size:var(--t-md);
  line-height:1.85;
  font-weight:400;
  overflow-x:hidden;
}
body::before{
  content:"";
  position:fixed;
  inset:0;
  z-index:-1;
  pointer-events:none;
  background-image:
    linear-gradient(to right, rgba(42,63,85,.32) 1px, transparent 1px),
    linear-gradient(to bottom, rgba(42,63,85,.32) 1px, transparent 1px);
  background-size:88px 88px;
  -webkit-mask-image:radial-gradient(130% 95% at 50% 0%, #000 0%, rgba(0,0,0,.35) 55%, transparent 82%);
  mask-image:radial-gradient(130% 95% at 50% 0%, #000 0%, rgba(0,0,0,.35) 55%, transparent 82%);
  opacity:.7;
}
h1,h2,h3,h4{line-height:1.18;margin:0 0 .6em}
p{margin:0 0 1em}
img,svg,video{max-width:100%}
ul,ol{margin:0 0 1em;padding-left:1.2em}
a{color:var(--cyan);text-decoration-thickness:1px;text-underline-offset:3px}
button{font-family:inherit}
:focus-visible{outline:2px solid var(--cyan);outline-offset:2px;border-radius:2px}

/* ----- 排版工具 ----- */
.mono{font-family:var(--mono);font-variant-numeric:tabular-nums;letter-spacing:.02em}
.index-label{
  display:inline-flex;align-items:center;gap:10px;
  font-family:var(--mono);font-size:var(--t-label);letter-spacing:.16em;
  color:var(--amber);text-transform:uppercase;margin:0 0 14px;
}
.index-label::before{content:"";width:22px;height:1px;background:var(--amber);opacity:.75}
.display-title{
  font-size:clamp(32px,5.4vw,72px);
  font-weight:900;letter-spacing:-0.02em;line-height:1.06;
  margin:0 0 .5em;color:var(--text);
}
.display-title em{font-style:normal;color:var(--cyan)}
.section-head{
  display:flex;align-items:flex-end;justify-content:space-between;
  gap:24px;flex-wrap:wrap;
  padding-bottom:16px;margin-bottom:28px;border-bottom:1px solid var(--line);
}
.section-head h2{font-size:clamp(22px,2.6vw,28px);font-weight:900;letter-spacing:-0.01em;margin:0}
.section-head p{margin:0;font-size:var(--t-xs);letter-spacing:.06em;color:var(--text-mute)}
.visually-hidden{
  position:absolute!important;width:1px;height:1px;padding:0;margin:-1px;
  overflow:hidden;clip:rect(0 0 0 0);white-space:nowrap;border:0;
}
.is-hidden{display:none!important}

/* ----- 版心与栅格 ----- */
.wrap{width:var(--shell);margin-inline:auto}
.grid-12{display:grid;grid-template-columns:repeat(12,minmax(0,1fr));gap:24px}

/* ----- 跳转链接 ----- */
.skip-link{
  position:absolute;left:16px;top:-72px;z-index:200;
  background:var(--cyan);color:#04121F;
  padding:10px 18px;border-radius:3px;
  font-size:var(--t-xs);font-weight:700;letter-spacing:.06em;
  text-decoration:none;
  transition:top var(--ease);
}
.skip-link:focus{top:12px}

/* ----- 头部 ----- */
.site-header{
  position:sticky;top:0;z-index:60;
  background:rgba(10,26,47,.88);
  -webkit-backdrop-filter:blur(14px) saturate(140%);
  backdrop-filter:blur(14px) saturate(140%);
  border-bottom:1px solid var(--line);
}
.header-rail{
  width:var(--shell);margin-inline:auto;
  display:flex;align-items:center;justify-content:space-between;
  gap:24px;min-height:72px;padding:10px 0;
}
.brand-cluster{display:flex;align-items:center;gap:20px;min-width:0}
.brand{
  display:inline-flex;align-items:center;gap:10px;
  padding:6px 0;text-decoration:none;color:var(--text);
}
.brand-mark{
  position:relative;flex:none;width:14px;height:14px;
  border:2px solid var(--cyan);
}
.brand-mark::after{content:"";position:absolute;inset:3px;background:var(--amber)}
.brand-name{
  font-size:var(--t-lg);font-weight:900;letter-spacing:-0.01em;
  line-height:1.1;white-space:nowrap;
}
.brand-version{
  font-family:var(--mono);font-size:11px;letter-spacing:.14em;
  color:var(--cyan);border:1px solid var(--line);border-radius:2px;
  padding:2px 6px;white-space:nowrap;
}
.cta-login{
  display:inline-flex;align-items:center;gap:8px;
  border:1px solid var(--coral);border-radius:3px;
  color:var(--coral);background:transparent;
  font-size:var(--t-xs);font-weight:700;letter-spacing:.04em;
  padding:7px 14px;text-decoration:none;white-space:nowrap;
  transition:background var(--ease),color var(--ease),box-shadow var(--ease),border-color var(--ease);
}
.cta-login::before{content:"";flex:none;width:6px;height:6px;border-radius:50%;background:var(--coral)}
.cta-login:hover,.cta-login:focus-visible{
  background:rgba(255,107,74,.16);
  border-color:var(--coral);
  color:#FFD9CF;
  box-shadow:0 0 0 3px rgba(255,107,74,.14);
}

/* ----- 导航 ----- */
.nav-toggle{
  display:none;align-items:center;gap:10px;
  background:transparent;border:1px solid var(--line);border-radius:3px;
  color:var(--text);font-size:var(--t-xs);letter-spacing:.08em;
  padding:9px 14px;cursor:pointer;
  transition:border-color var(--ease),background var(--ease),color var(--ease);
}
.nav-toggle:hover,.nav-toggle:focus-visible{border-color:var(--cyan);color:var(--cyan)}
.nav-toggle-label{display:inline}
.nav-toggle-bars{position:relative;flex:none;width:16px;height:10px}
.nav-toggle-bars::before,.nav-toggle-bars::after{
  content:"";position:absolute;left:0;right:0;height:1.5px;background:var(--cyan);
  transition:transform var(--ease);
}
.nav-toggle-bars::before{top:0}
.nav-toggle-bars::after{bottom:0}
.nav-toggle[aria-expanded="true"] .nav-toggle-bars::before{transform:translateY(4px) rotate(45deg)}
.nav-toggle[aria-expanded="true"] .nav-toggle-bars::after{transform:translateY(-4px) rotate(-45deg)}

.site-nav{display:block}
.nav-list{
  display:flex;align-items:center;gap:26px;
  list-style:none;margin:0;padding:0;counter-reset:navidx;
}
.nav-list>li{counter-increment:navidx;min-width:0}
.nav-list a{
  position:relative;display:inline-flex;align-items:baseline;gap:7px;
  padding:8px 0 9px;
  font-size:var(--t-xs);letter-spacing:.08em;
  color:var(--text-mute);text-decoration:none;
  transition:color var(--ease);
}
.nav-list a::before{
  content:counter(navidx, decimal-leading-zero);
  font-family:var(--mono);font-size:10px;letter-spacing:.06em;
  color:var(--amber);opacity:.72;
  transition:color var(--ease),opacity var(--ease);
}
.nav-list a::after{
  content:"";position:absolute;left:0;right:0;bottom:0;height:2px;
  background:var(--cyan);transform:scaleX(0);transform-origin:left;
  transition:transform 180ms cubic-bezier(.4,0,.2,1);
}
.nav-list a:hover,.nav-list a:focus-visible{color:var(--text)}
.nav-list a:hover::after,.nav-list a:focus-visible::after{transform:scaleX(1)}
.nav-list a[aria-current="page"]{color:var(--text);font-weight:700}
.nav-list a[aria-current="page"]::before{color:var(--cyan);opacity:1}
.nav-list a[aria-current="page"]::after{transform:scaleX(1)}

/* ----- 页脚 ----- */
.site-footer{
  position:relative;z-index:1;
  margin-top:88px;
  border-top:1px solid var(--line);
  background:linear-gradient(180deg, rgba(16,36,61,.55), rgba(10,26,47,1));
}
.footer-rail{
  width:var(--shell);margin-inline:auto;
  display:grid;grid-template-columns:1.1fr 1fr 1.3fr;gap:32px;
  padding:56px 0 34px;
}
.footer-col{min-width:0}
.footer-col p{margin:0 0 10px;font-size:var(--t-xs);color:var(--text-mute)}
.footer-heading{
  font-size:var(--t-label);letter-spacing:.14em;text-transform:uppercase;
  font-weight:600;color:var(--text-mute);
  margin:0 0 18px;padding-bottom:10px;border-bottom:1px solid var(--line);
}
.footer-links{list-style:none;margin:0;padding:0;display:grid;gap:10px}
.footer-links a{
  display:inline-flex;align-items:center;
  color:var(--text-mute);text-decoration:none;
  font-size:14px;line-height:1.6;
  transition:color var(--ease);
}
.footer-links a::before{
  content:"";display:inline-block;width:0;height:1px;
  background:var(--cyan);vertical-align:middle;
  transition:width var(--ease),margin-right var(--ease);
}
.footer-links a:hover,.footer-links a:focus-visible{color:var(--cyan)}
.footer-links a:hover::before,.footer-links a:focus-visible::before{width:10px;margin-right:7px}
.footer-links--plain li{
  display:flex;flex-wrap:wrap;align-items:baseline;gap:10px;
  font-size:14px;color:var(--text-mute);line-height:1.7;
}
.footer-links--plain a::before{display:none}
.footer-key{
  font-family:var(--mono);font-size:var(--t-label);letter-spacing:.08em;
  color:var(--amber);min-width:62px;
}
.footer-status{
  width:var(--shell);margin-inline:auto;
  border-top:1px solid var(--line);
  padding:16px 0 26px;
  display:flex;flex-wrap:wrap;gap:8px 28px;
  font-family:var(--mono);font-size:var(--t-label);
  letter-spacing:.08em;color:var(--text-mute);
}
.status-key{color:var(--amber)}

/* ----- 通用按钮 ----- */
.btn{
  display:inline-flex;align-items:center;gap:8px;
  font-size:14px;font-weight:700;letter-spacing:.04em;
  padding:11px 20px;border-radius:3px;
  border:1px solid var(--line);background:transparent;color:var(--text);
  text-decoration:none;cursor:pointer;
  transition:background var(--ease),border-color var(--ease),color var(--ease),box-shadow var(--ease);
}
.btn--primary{background:var(--cyan);border-color:var(--cyan);color:#04121F}
.btn--primary:hover,.btn--primary:focus-visible{background:var(--cyan-hover);border-color:var(--cyan-hover)}
.btn--ghost{color:var(--text-mute)}
.btn--ghost:hover,.btn--ghost:focus-visible{border-color:var(--cyan);color:var(--cyan)}
.btn--coral{border-color:var(--coral);color:var(--coral)}
.btn--coral:hover,.btn--coral:focus-visible{background:rgba(255,107,74,.14);color:#FFD9CF}

/* ----- 面包屑 ----- */
.breadcrumb{font-family:var(--mono);font-size:var(--t-label);letter-spacing:.08em;color:var(--text-mute);margin-bottom:22px}
.breadcrumb ol{display:flex;flex-wrap:wrap;gap:8px;list-style:none;margin:0;padding:0}
.breadcrumb li+li::before{content:"/";margin-right:8px;color:var(--line)}
.breadcrumb a{color:var(--text-mute);text-decoration:none}
.breadcrumb a:hover,.breadcrumb a:focus-visible{color:var(--cyan)}

/* ----- 正文容器 ----- */
.prose{max-width:74ch;font-size:var(--t-md);line-height:1.85;color:var(--text)}
.prose h2{font-size:var(--t-xl);font-weight:900;letter-spacing:-0.01em;margin:2.2em 0 .7em}
.prose h3{font-size:var(--t-lg);font-weight:700;margin:1.8em 0 .6em}
.prose ul,.prose ol{padding-left:1.3em}
.prose li{margin-bottom:.45em}
.prose a{color:var(--cyan)}

/* ----- 内容层：实色 / 玻璃 ----- */
.panel{
  background:var(--ink-800);
  border:1px solid var(--line);
  border-radius:4px;
  padding:22px;
  transition:border-color var(--ease),transform var(--ease),box-shadow var(--ease);
}
.panel:hover{border-color:var(--cyan);transform:translateY(-2px);box-shadow:0 18px 40px -26px rgba(0,229,200,.55)}
.panel--glass{
  background:rgba(22,50,79,.55);
  -webkit-backdrop-filter:blur(12px);
  backdrop-filter:blur(12px);
  border-color:rgba(42,63,85,.9);
}

/* ----- 标签 ----- */
.tag{
  display:inline-flex;align-items:center;gap:6px;
  font-size:var(--t-label);letter-spacing:.06em;
  padding:4px 10px;border:1px solid var(--line);border-radius:999px;
  color:var(--text-mute);background:rgba(22,50,79,.5);
}
.tag--accent{border-color:rgba(255,179,71,.6);color:var(--amber)}

/* ----- 筛选 ----- */
.filter-bar{display:flex;flex-wrap:wrap;gap:10px}
.filter-chip{
  font:inherit;font-size:var(--t-xs);letter-spacing:.06em;
  padding:8px 15px;border:1px solid var(--line);border-radius:3px;
  background:transparent;color:var(--text-mute);cursor:pointer;
  transition:background var(--ease),border-color var(--ease),color var(--ease);
}
.filter-chip:hover,.filter-chip:focus-visible{color:var(--text);border-color:var(--cyan-hover)}
.filter-chip.is-active{background:rgba(0,229,200,.12);border-color:var(--cyan);color:var(--cyan)}

/* ----- 纵向索引 ----- */
.toc{list-style:none;margin:0;padding:0;display:grid;gap:2px;counter-reset:tocidx}
.toc a{
  display:flex;gap:10px;
  padding:9px 10px;
  color:var(--text-mute);text-decoration:none;font-size:14px;line-height:1.6;
  border-left:2px solid transparent;
  transition:color var(--ease),border-color var(--ease),background var(--ease);
}
.toc a::before{
  counter-increment:tocidx;
  content:counter(tocidx, decimal-leading-zero);
  font-family:var(--mono);font-size:11px;color:var(--amber);
}
.toc a:hover,.toc a:focus-visible,.toc a[aria-current="true"]{
  color:var(--text);border-left-color:var(--cyan);background:rgba(0,229,200,.06);
}
.toc a[aria-current="true"]::before{color:var(--cyan)}

/* ----- 横向步骤轨道 ----- */
.step-track{
  position:relative;display:flex;
  overflow-x:auto;
  list-style:none;margin:0;padding:0;
  border-top:1px solid var(--line);border-bottom:1px solid var(--line);
  scrollbar-width:thin;
}
.step-node{
  position:relative;flex:1 0 220px;
  padding:22px 22px 24px;
  border-right:1px solid var(--line);
}
.step-node:last-child{border-right:0}
.step-num{
  display:block;margin-bottom:8px;line-height:1;
  font-family:var(--mono);font-size:26px;color:var(--amber);
}
.step-node::before{
  content:"";position:absolute;left:0;top:-1px;height:2px;width:0;
  background:var(--cyan);transition:width 240ms ease;
}
.step-node:hover::before,.step-node[data-active]::before{width:100%}

/* ----- 媒体容器 ----- */
.media-frame{
  position:relative;display:block;overflow:hidden;
  aspect-ratio:16/9;
  border:1px solid var(--line);border-radius:4px;
  background:linear-gradient(150deg,var(--ink-700),var(--ink-800));
}
.media-frame img,.media-frame video{display:block;width:100%;height:100%;object-fit:cover}
.media-frame::after{
  content:"";position:absolute;left:0;right:0;bottom:0;height:2px;
  background:linear-gradient(90deg,var(--cyan),transparent);
}
.media-frame--wide{aspect-ratio:21/9}
.media-frame--tall{aspect-ratio:4/5}
.media-frame--square{aspect-ratio:1/1}

/* ----- 滚动进度 ----- */
.scroll-progress{
  position:fixed;top:0;left:0;z-index:120;
  width:100%;height:2px;
  background:linear-gradient(90deg,var(--cyan),var(--amber));
  transform:scaleX(0);transform-origin:0 50%;
  pointer-events:none;
}

/* ----- 响应式 ----- */
@media (max-width:1100px){
  .nav-list{gap:18px}
  .footer-rail{grid-template-columns:1fr 1fr;gap:32px 40px}
}

@media (max-width:960px){
  :root{--shell:min(1280px, calc(100% - 32px))}
  .grid-12{grid-template-columns:repeat(6,minmax(0,1fr))}
  .header-rail{min-height:64px;padding:8px 0}
  .nav-toggle{display:inline-flex}
  .site-nav{
    position:absolute;left:0;right:0;top:100%;
    background:rgba(16,36,61,.98);
    -webkit-backdrop-filter:blur(16px);
    backdrop-filter:blur(16px);
    border-bottom:1px solid var(--line);
    padding:6px 0 14px;
    opacity:0;visibility:hidden;transform:translateY(-8px);
    transition:opacity var(--ease),transform var(--ease),visibility var(--ease);
  }
  .site-nav[data-open]{opacity:1;visibility:visible;transform:translateY(0)}
  .nav-list{
    flex-direction:column;align-items:stretch;gap:0;
    width:var(--shell);margin-inline:auto;
  }
  .nav-list a{
    width:100%;padding:14px 4px 15px;font-size:var(--t-sm);
    border-bottom:1px solid rgba(42,63,85,.6);
  }
  .nav-list a::after{bottom:-1px;left:4px;right:auto;width:56px}
  .footer-rail{grid-template-columns:1fr;gap:34px;padding:44px 0 28px}
  .site-footer{margin-top:64px}
}

@media (max-width:640px){
  .grid-12{grid-template-columns:repeat(2,minmax(0,1fr))}
  .brand-cluster{gap:12px}
  .brand-name{font-size:var(--t-md)}
  .brand-version{display:none}
  .cta-login{padding:6px 10px;font-size:var(--t-label);letter-spacing:.02em}
  .nav-toggle-label{display:none}
  .footer-status{flex-direction:column;gap:6px}
}

/* ----- 无障碍与减退动效 ----- */
@media (prefers-reduced-motion: reduce){
  html{scroll-behavior:auto}
  *,*::before,*::after{
    transition-duration:.001ms!important;
    animation-duration:.001ms!important;
    animation-iteration-count:1!important;
  }
  .panel:hover{transform:none}
}