:root{
  --brand-950:#082f49;
  --brand-900:#0a4666;
  --brand-800:#0b5c7f;
  --brand-700:#0b7397;
  --brand-600:#0e88aa;
  --brand-100:#dff4f7;
  --brand-50:#f0fafb;
  --ink:#142536;
  --muted:#607385;
  --line:#dce5ec;
  --surface:#ffffff;
  --surface-2:#f5f8fb;
  --warning:#e9a23b;
  --danger:#d95843;
  --success:#168c62;
  --shadow:0 12px 35px rgba(18,54,79,.09);
  --radius:18px;
  --sidebar:310px;
  --toc:225px;
}
*{box-sizing:border-box}
html{scroll-behavior:smooth}
body{
  margin:0;
  font-family:Inter,ui-sans-serif,system-ui,-apple-system,BlinkMacSystemFont,"Segoe UI",sans-serif;
  color:var(--ink);
  background:var(--surface-2);
  line-height:1.65;
}
a{color:var(--brand-700);text-decoration:none}
a:hover{color:var(--brand-900)}
button,input{font:inherit}
button{cursor:pointer}
.skip-link{
  position:fixed;left:16px;top:-80px;z-index:1000;
  background:#fff;padding:10px 16px;border-radius:10px;box-shadow:var(--shadow)
}
.skip-link:focus{top:16px}
.site-header{
  height:74px;background:rgba(255,255,255,.96);backdrop-filter:blur(12px);
  border-bottom:1px solid var(--line);position:sticky;top:0;z-index:50;
}
.header-inner{
  max-width:1700px;height:100%;margin:auto;padding:0 28px;
  display:grid;grid-template-columns:auto minmax(260px,650px) auto;gap:28px;align-items:center;
}
.brand{display:flex;align-items:center;gap:12px;color:var(--ink);font-weight:800;white-space:nowrap}
.brand img{width:42px;height:42px}
.brand-copy{display:flex;flex-direction:column;line-height:1.05}
.brand-copy small{font-size:11px;letter-spacing:.12em;color:var(--brand-700);text-transform:uppercase;margin-bottom:4px}
.search-shell{position:relative}
.search-shell svg{position:absolute;left:16px;top:50%;transform:translateY(-50%);width:20px;color:var(--muted)}
.global-search{
  width:100%;height:46px;border:1px solid var(--line);border-radius:14px;padding:0 44px;
  background:var(--surface-2);outline:none;transition:.2s
}
.global-search:focus{background:#fff;border-color:var(--brand-600);box-shadow:0 0 0 4px rgba(14,136,170,.13)}
.search-shortcut{position:absolute;right:12px;top:50%;transform:translateY(-50%);font-size:12px;color:var(--muted);border:1px solid var(--line);border-radius:7px;padding:2px 7px;background:#fff}
.header-actions{display:flex;align-items:center;gap:9px}
.action-link{padding:10px 12px;border-radius:11px;color:var(--ink);font-weight:650;font-size:14px;white-space:nowrap}
.action-link:hover{background:var(--surface-2)}
.action-link.primary{background:var(--brand-800);color:#fff}
.action-link.primary:hover{background:var(--brand-950);color:#fff}
.icon-button{
  width:42px;height:42px;border:1px solid var(--line);background:#fff;border-radius:12px;
  display:none;align-items:center;justify-content:center;color:var(--ink)
}
.layout{
  max-width:1700px;margin:auto;display:grid;grid-template-columns:var(--sidebar) minmax(0,1fr) var(--toc);
  min-height:calc(100vh - 74px)
}
.sidebar{
  border-right:1px solid var(--line);padding:27px 22px 60px;background:#f9fbfd;
  position:sticky;top:74px;height:calc(100vh - 74px);overflow:auto
}
.sidebar-top{display:flex;align-items:center;justify-content:space-between;margin-bottom:20px}
.sidebar-title{font-size:12px;letter-spacing:.13em;text-transform:uppercase;color:var(--muted);font-weight:800}
.tree-section{margin-bottom:7px}
.tree-section-btn{
  width:100%;border:0;background:transparent;display:flex;align-items:center;gap:10px;
  padding:10px 10px;border-radius:10px;color:var(--ink);text-align:left;font-weight:730
}
.tree-section-btn:hover{background:#eaf3f7}
.tree-section-btn svg{width:17px;flex:0 0 auto;transition:.2s}
.tree-section.open .tree-section-btn svg{transform:rotate(90deg)}
.tree-items{display:none;padding:2px 0 7px 37px}
.tree-section.open .tree-items{display:block}
.tree-subtitle{font-size:11px;text-transform:uppercase;letter-spacing:.08em;color:#8595a4;font-weight:800;margin:9px 0 4px}
.tree-link{display:block;padding:7px 9px;border-radius:8px;font-size:14px;line-height:1.35;color:#43576a}
.tree-link:hover,.tree-link.active{background:var(--brand-100);color:var(--brand-950)}
.sidebar-note{
  margin-top:24px;border:1px solid #c8e8ee;background:var(--brand-50);padding:15px;border-radius:14px;
  font-size:13px;color:#31586a
}
.sidebar-note strong{display:block;color:var(--brand-950);margin-bottom:4px}
.main{min-width:0;padding:42px clamp(28px,5vw,76px) 80px;background:#fff}
.content{max-width:940px;margin:0 auto}
.toc{
  border-left:1px solid var(--line);padding:34px 22px;position:sticky;top:74px;height:calc(100vh - 74px);
  overflow:auto;background:#fff
}
.toc h2{font-size:12px;letter-spacing:.12em;text-transform:uppercase;color:var(--muted);margin:0 0 16px}
.toc a{display:block;font-size:13px;color:#64788a;padding:5px 0 5px 11px;border-left:2px solid transparent;line-height:1.35}
.toc a:hover,.toc a.active{color:var(--brand-800);border-left-color:var(--brand-600)}
.breadcrumbs{display:flex;gap:8px;align-items:center;color:var(--muted);font-size:13px;margin-bottom:24px;flex-wrap:wrap}
.breadcrumbs span{color:#9babb8}
.hero{
  background:linear-gradient(135deg,var(--brand-950),var(--brand-700));
  color:#fff;border-radius:26px;padding:clamp(30px,5vw,58px);box-shadow:var(--shadow);overflow:hidden;position:relative
}
.hero:after{
  content:"";position:absolute;width:330px;height:330px;border:60px solid rgba(255,255,255,.06);
  border-radius:50%;right:-130px;top:-140px
}
.eyebrow{display:inline-flex;align-items:center;gap:8px;font-weight:800;text-transform:uppercase;letter-spacing:.11em;font-size:12px;color:#b8edf3}
.hero h1{font-size:clamp(36px,5vw,62px);line-height:1.06;margin:13px 0 18px;max-width:760px}
.hero p{font-size:18px;max-width:760px;color:#d9edf3;margin:0}
.hero-actions{display:flex;gap:12px;margin-top:28px;flex-wrap:wrap}
.btn{
  display:inline-flex;align-items:center;justify-content:center;gap:8px;border:0;border-radius:12px;
  padding:12px 17px;font-weight:760
}
.btn-light{background:#fff;color:var(--brand-950)}
.btn-ghost{background:rgba(255,255,255,.11);color:#fff;border:1px solid rgba(255,255,255,.22)}
.quick-grid{display:grid;grid-template-columns:repeat(3,minmax(0,1fr));gap:16px;margin:25px 0 40px}
.metric{padding:18px;border:1px solid var(--line);border-radius:16px;background:#fff}
.metric strong{font-size:26px;color:var(--brand-900);display:block}
.metric span{font-size:13px;color:var(--muted)}
.section-heading{display:flex;align-items:end;justify-content:space-between;gap:20px;margin:50px 0 18px}
.section-heading h2{font-size:28px;line-height:1.2;margin:0}
.section-heading p{margin:5px 0 0;color:var(--muted)}
.card-grid{display:grid;grid-template-columns:repeat(2,minmax(0,1fr));gap:16px}
.topic-card{
  border:1px solid var(--line);border-radius:18px;padding:21px;background:#fff;
  transition:.2s;display:flex;gap:15px;color:var(--ink)
}
.topic-card:hover{transform:translateY(-3px);box-shadow:var(--shadow);border-color:#b9dce4;color:var(--ink)}
.topic-icon{width:45px;height:45px;border-radius:13px;background:var(--brand-50);display:flex;align-items:center;justify-content:center;color:var(--brand-700);flex:none;font-weight:900}
.topic-card h3{font-size:17px;line-height:1.25;margin:0 0 7px}
.topic-card p{font-size:13px;color:var(--muted);margin:0}
.progress-list{display:grid;gap:10px}
.progress-link{
  display:flex;align-items:center;gap:13px;padding:14px 16px;border:1px solid var(--line);border-radius:14px;color:var(--ink)
}
.progress-link:hover{background:var(--brand-50);color:var(--ink)}
.number{width:30px;height:30px;border-radius:10px;background:#e8f4f7;color:var(--brand-800);display:flex;align-items:center;justify-content:center;font-size:12px;font-weight:850;flex:none}
.progress-link small{margin-left:auto;color:var(--muted)}
.search-results{display:none;margin:18px 0 35px;border:1px solid var(--line);border-radius:16px;overflow:hidden}
.search-results.visible{display:block}
.search-result{display:block;padding:14px 17px;border-bottom:1px solid var(--line);color:var(--ink);background:#fff}
.search-result:last-child{border-bottom:0}
.search-result:hover{background:var(--brand-50);color:var(--ink)}
.search-result strong{display:block}
.search-result span{font-size:12px;color:var(--muted)}
.article-header h1{font-size:clamp(36px,5vw,58px);line-height:1.08;letter-spacing:-.025em;margin:0 0 18px}
.article-lead{font-size:20px;color:#4b6174;max-width:800px}
.article-meta{display:flex;gap:15px;flex-wrap:wrap;margin:23px 0 34px;color:var(--muted);font-size:13px}
.badge{display:inline-flex;padding:5px 10px;border-radius:999px;background:var(--brand-50);color:var(--brand-800);font-weight:760}
.answer-box{
  background:linear-gradient(135deg,#eaf8fa,#f7fbfc);border:1px solid #bfe7ed;border-left:5px solid var(--brand-600);
  border-radius:17px;padding:25px;margin:28px 0 34px
}
.answer-box h2{font-size:14px;letter-spacing:.09em;text-transform:uppercase;color:var(--brand-800);margin:0 0 10px}
.answer-box p{font-size:19px;line-height:1.55;margin:0;color:#1e4355}
.article-body h2{font-size:30px;line-height:1.2;margin:52px 0 16px;scroll-margin-top:105px}
.article-body h3{font-size:21px;line-height:1.25;margin:32px 0 10px;scroll-margin-top:105px}
.article-body p,.article-body li{font-size:17px}
.article-body ul{padding-left:22px}
.callout{border:1px solid #efd8ab;background:#fff9ec;border-radius:15px;padding:18px 20px;margin:24px 0}
.callout strong{color:#8a5a08}
.figure{margin:28px 0}
.figure img{width:100%;border:1px solid var(--line);border-radius:20px;display:block;background:#f5f8fb}
.figure figcaption{font-size:13px;color:var(--muted);margin-top:9px}
.formula{font-family:"SFMono-Regular",Consolas,monospace;font-size:21px;background:#102e41;color:#fff;padding:20px;border-radius:14px;text-align:center;margin:20px 0}
.quiz{display:grid;gap:12px;margin-top:20px}
.quiz details{border:1px solid var(--line);border-radius:14px;padding:0 17px;background:#fff}
.quiz summary{padding:15px 0;font-weight:760;cursor:pointer}
.quiz details p{font-size:15px;color:#4f6577;padding-bottom:15px;margin:0}
.footer-nav{display:grid;grid-template-columns:1fr 1fr;gap:14px;margin-top:55px;padding-top:25px;border-top:1px solid var(--line)}
.footer-nav a{border:1px solid var(--line);border-radius:15px;padding:16px;color:var(--ink)}
.footer-nav a:last-child{text-align:right}
.footer-nav span{display:block;font-size:12px;color:var(--muted)}
.placeholder{
  border:1px dashed #b7c9d6;border-radius:18px;padding:36px;background:#f8fafc;text-align:center;color:var(--muted)
}
.site-footer{margin-top:60px;border-top:1px solid var(--line);padding:25px 0;color:var(--muted);font-size:13px}
.overlay{display:none}
@media(max-width:1230px){
  :root{--toc:0px}
  .layout{grid-template-columns:var(--sidebar) minmax(0,1fr)}
  .toc{display:none}
}
@media(max-width:900px){
  .site-header{height:66px}
  .header-inner{grid-template-columns:auto 1fr auto;padding:0 16px;gap:13px}
  .brand-copy small{display:none}
  .brand-copy span{font-size:15px}
  .brand img{width:38px;height:38px}
  .search-shell{order:4;position:absolute;left:0;right:0;top:66px;padding:10px 16px;background:#fff;border-bottom:1px solid var(--line);display:none}
  .search-shell.open{display:block}
  .header-actions .action-link{display:none}
  .icon-button{display:flex}
  .layout{display:block;padding-top:67px}
  .sidebar{
    position:fixed;z-index:80;left:0;top:0;width:min(88vw,360px);height:100vh;transform:translateX(-103%);
    transition:.25s;box-shadow:var(--shadow);padding-top:90px
  }
  .sidebar.open{transform:translateX(0)}
  .overlay{position:fixed;inset:0;background:rgba(8,30,45,.45);z-index:70}
  .overlay.open{display:block}
  .main{padding:28px 20px 60px}
  .quick-grid{grid-template-columns:1fr}
  .card-grid{grid-template-columns:1fr}
  .hero{border-radius:20px}
  .footer-nav{grid-template-columns:1fr}
  .footer-nav a:last-child{text-align:left}
}
@media(max-width:560px){
  .hero h1{font-size:38px}
  .hero p{font-size:16px}
  .article-header h1{font-size:38px}
  .article-lead{font-size:17px}
  .section-heading{align-items:flex-start;flex-direction:column}
}