/* ============ 设计变量 ============ */
:root{
  --paper:#FBFAF6;
  --paper-2:#F4F1E9;
  --surface:#FFFFFF;
  --ink:#1B1F24;
  --ink-2:#414A53;
  --muted:#77818B;
  --line:#E7E2D6;
  --line-2:#F0ECE2;
  --accent:#1E5A8A;
  --accent-2:#2E7BA8;
  --accent-soft:#EAF2F8;
  --seal:#B3452C;
  --seal-soft:#FAEEE9;
  --green:#2F6B4F;
  --green-soft:#EBF4EF;
  --shadow-sm:0 1px 2px rgba(27,31,36,.05), 0 2px 8px rgba(27,31,36,.04);
  --shadow-md:0 2px 6px rgba(27,31,36,.06), 0 12px 32px rgba(27,31,36,.07);
  --serif:"Iowan Old Style","Palatino Linotype","Source Han Serif SC","Noto Serif SC","Songti SC",Georgia,"Times New Roman",serif;
  --sans:-apple-system,BlinkMacSystemFont,"Segoe UI","Microsoft YaHei","PingFang SC","Hiragino Sans GB",sans-serif;
  --mono:"SFMono-Regular",Consolas,"Liberation Mono",Menlo,monospace;
  --r:14px;
}

*{box-sizing:border-box}
html,body{height:100%}
body{
  margin:0;
  font-family:var(--sans);
  background:var(--paper);
  color:var(--ink);
  -webkit-font-smoothing:antialiased;
  text-rendering:optimizeLegibility;
}
a{color:inherit;text-decoration:none}
button{font-family:inherit;cursor:pointer;border:0;background:none;color:inherit}
::selection{background:#CFE3F2;color:#10314B}

/* 滚动条 */
.scroller::-webkit-scrollbar,.nav::-webkit-scrollbar,.modal-results::-webkit-scrollbar{width:10px}
.scroller::-webkit-scrollbar-thumb,.nav::-webkit-scrollbar-thumb,.modal-results::-webkit-scrollbar-thumb{
  background:#DAD4C6;border-radius:10px;border:3px solid transparent;background-clip:content-box
}
.scroller::-webkit-scrollbar-thumb:hover,.nav::-webkit-scrollbar-thumb:hover{background:#C6BFAD;background-clip:content-box}

/* ============ 布局 ============ */
.app{
  display:grid;
  grid-template-columns:274px minmax(0,1fr);
  height:100vh;
  overflow:hidden;
}

/* ============ 侧栏 ============ */
.sidebar{
  display:flex;flex-direction:column;
  background:linear-gradient(180deg,#F7F4EC 0%,#F3EFE5 100%);
  border-right:1px solid var(--line);
  height:100vh;
  z-index:40;
}
.brand{
  display:flex;align-items:center;gap:12px;
  padding:22px 20px 18px;
  border-bottom:1px solid rgba(231,226,214,.8);
}
.brand-mark{
  width:38px;height:38px;flex:0 0 38px;
  display:grid;place-items:center;
  background:var(--ink);color:#F7F4EC;
  border-radius:11px;
  font-family:var(--serif);font-size:22px;line-height:1;
  padding-top:2px;
  box-shadow:0 1px 0 rgba(255,255,255,.4) inset, 0 4px 12px rgba(27,31,36,.14);
}
.brand-text{display:flex;flex-direction:column;line-height:1.25;min-width:0}
.brand-text strong{font-family:var(--serif);font-size:17px;letter-spacing:.06em;font-weight:600}
.brand-text em{font-style:normal;font-size:10.5px;color:var(--muted);letter-spacing:.14em;text-transform:uppercase;margin-top:2px}

.nav{flex:1;overflow-y:auto;padding:14px 12px 8px}
.nav-group{margin-bottom:14px}
.nav-label{
  font-size:10.5px;letter-spacing:.16em;text-transform:uppercase;
  color:#9A9284;padding:8px 10px 6px;font-weight:600;
}
.nav-item{
  display:flex;align-items:center;gap:9px;
  padding:7px 10px;border-radius:9px;
  font-size:13.5px;color:var(--ink-2);
  transition:background .16s,color .16s;
  position:relative;
}
.nav-item:hover{background:rgba(255,255,255,.75);color:var(--ink)}
.nav-item.active{background:var(--surface);color:var(--ink);font-weight:600;box-shadow:var(--shadow-sm)}
.nav-item.active::before{
  content:"";position:absolute;left:-12px;top:50%;transform:translateY(-50%);
  width:2.5px;height:16px;border-radius:2px;background:var(--accent);
}
.nav-no{
  font-family:var(--serif);font-size:11.5px;color:#A39B8C;
  width:16px;flex:0 0 16px;text-align:right;font-variant-numeric:tabular-nums;
}
.nav-item.active .nav-no{color:var(--accent)}
.nav-item .dot{
  margin-left:auto;width:6px;height:6px;border-radius:50%;
  background:var(--green);opacity:0;transition:opacity .2s;
}
.nav-item.done .dot{opacity:1}

.side-foot{padding:14px 16px 18px;border-top:1px solid rgba(231,226,214,.9)}
.prog-head{display:flex;justify-content:space-between;font-size:11px;color:var(--muted);margin-bottom:7px;letter-spacing:.04em}
.prog-head span:last-child{font-variant-numeric:tabular-nums;color:var(--ink-2);font-weight:600}
.prog-bar{height:5px;background:#E4F0E9;border-radius:99px;overflow:hidden}
.prog-bar i{display:block;height:100%;width:0;background:linear-gradient(90deg,#4E9673,#2F6B4F);border-radius:99px;transition:width .5s cubic-bezier(.2,.7,.3,1)}
.side-note{font-size:10.5px;color:#9A9284;line-height:1.6;margin:12px 0 0}

.sidebar-scrim{
  display:none;position:fixed;inset:0;background:rgba(27,31,36,.32);
  backdrop-filter:blur(2px);z-index:35;
}

/* ============ 主区域 ============ */
.main{display:grid;grid-template-columns:minmax(0,1fr) 216px;grid-template-rows:auto minmax(0,1fr);height:100vh;overflow:hidden}

.topbar{
  grid-column:1/-1;
  display:flex;align-items:center;gap:14px;
  padding:0 28px;height:60px;
  border-bottom:1px solid var(--line);
  background:rgba(251,250,246,.86);
  backdrop-filter:saturate(180%) blur(10px);
  position:relative;z-index:20;
}
.crumbs{font-size:12.5px;color:var(--muted);display:flex;align-items:center;gap:8px;min-width:0;white-space:nowrap;overflow:hidden}
.crumbs b{color:var(--ink);font-weight:600}
.crumbs .sep{color:#CFC8B9}
.icon-btn{
  width:32px;height:32px;border-radius:8px;display:grid;place-items:center;
  color:var(--ink-2);font-size:15px;transition:background .15s;
}
.icon-btn:hover{background:var(--paper-2)}
.menu-btn{display:none;font-size:17px}

.search-trigger{
  margin-left:auto;
  display:flex;align-items:center;gap:8px;
  height:34px;padding:0 10px 0 11px;
  border:1px solid var(--line);border-radius:9px;
  background:var(--surface);
  color:var(--muted);font-size:12.5px;
  transition:border-color .15s,box-shadow .15s;
  max-width:340px;
}
.search-trigger:hover{border-color:#D5CDBA;box-shadow:var(--shadow-sm);color:var(--ink-2)}
.search-trigger .st-icon{font-size:14px;color:#A39B8C}
kbd{
  font-family:var(--sans);font-size:10px;line-height:1;
  padding:3px 5px;border-radius:4px;
  background:var(--paper-2);border:1px solid var(--line);
  color:var(--muted);
}

.scroller{grid-column:1;overflow-y:auto;overflow-x:hidden;scroll-behavior:smooth}
.page{max-width:836px;margin:0 auto;padding:46px 44px 40px;min-height:70vh}

/* ============ 右侧页内目录 ============ */
.main.no-toc{grid-template-columns:minmax(0,1fr)}
.main.no-toc .toc{display:none}
.toc{
  grid-column:2;overflow-y:auto;padding:52px 22px 40px 4px;
  border-left:1px solid var(--line-2);
}
.toc-t{
  font-size:10.5px;letter-spacing:.14em;text-transform:uppercase;
  color:#9A9284;font-weight:600;margin:0 0 10px 12px;
}
.toc a{
  display:block;font-size:12px;color:var(--muted);line-height:1.45;
  padding:5px 10px 5px 12px;border-left:2px solid transparent;
  transition:color .15s,border-color .15s;
}
.toc a:hover{color:var(--ink)}
.toc a.on{color:var(--accent);border-left-color:var(--accent);font-weight:600}

/* ============ 首页 ============ */
.hero{
  position:relative;
  margin:0 0 44px;
  padding:58px 48px 44px;
  border:1px solid var(--line);
  border-radius:20px;
  box-shadow:var(--shadow-sm);
  background:
    radial-gradient(900px 300px at 12% -10%, #E9F1F7 0%, rgba(233,241,247,0) 62%),
    radial-gradient(500px 240px at 92% 10%, #F7EDE6 0%, rgba(247,237,230,0) 65%),
    var(--paper);
  overflow:hidden;
}
.hero::after{
  content:"";
  position:absolute;inset:0;
  background-image:linear-gradient(rgba(30,90,138,.055) 1px,transparent 1px),linear-gradient(90deg,rgba(30,90,138,.055) 1px,transparent 1px);
  background-size:28px 28px;
  mask-image:radial-gradient(680px 320px at 20% 0%,#000 0%,transparent 78%);
  -webkit-mask-image:radial-gradient(680px 320px at 20% 0%,#000 0%,transparent 78%);
  pointer-events:none;
}
.hero>*{position:relative;z-index:1}
.eyebrow{
  display:inline-flex;align-items:center;gap:8px;
  font-size:11px;letter-spacing:.18em;text-transform:uppercase;
  color:var(--accent);font-weight:600;margin-bottom:18px;
}
.eyebrow::before{content:"";width:22px;height:1px;background:var(--accent);opacity:.6}
.hero h1{
  font-family:var(--serif);
  font-size:clamp(34px,4.6vw,52px);
  line-height:1.18;letter-spacing:-.01em;
  margin:0 0 18px;font-weight:600;
}
.hero h1 em{
  font-style:italic;color:var(--accent);
  font-family:var(--serif);
}
.hero p.lead{
  font-size:15.5px;line-height:1.85;color:var(--ink-2);
  max-width:560px;margin:0 0 30px;
}
.hero p.lead b{font-weight:600;color:var(--ink)}
.hero-actions{display:flex;gap:12px;flex-wrap:wrap;align-items:center}
.btn{
  display:inline-flex;align-items:center;gap:8px;
  height:42px;padding:0 20px;border-radius:10px;
  font-size:13.5px;font-weight:600;letter-spacing:.01em;
  transition:transform .15s,box-shadow .2s,background .2s;
}
.btn-primary{background:var(--ink);color:#FBF9F4;box-shadow:0 2px 10px rgba(27,31,36,.18)}
.btn-primary:hover{transform:translateY(-1px);box-shadow:0 6px 18px rgba(27,31,36,.22)}
.btn-ghost{border:1px solid var(--line);background:var(--surface);color:var(--ink-2)}
.btn-ghost:hover{border-color:#D5CDBA;transform:translateY(-1px)}

.hero-meta{
  display:flex;gap:34px;margin-top:38px;padding-top:26px;
  border-top:1px dashed #DCD5C4;flex-wrap:wrap;
}
.hero-meta div{display:flex;flex-direction:column;gap:3px}
.hero-meta strong{font-family:var(--serif);font-size:22px;font-weight:600;letter-spacing:-.01em}
.hero-meta span{font-size:11px;color:var(--muted);letter-spacing:.06em}

/* 首页小节标题 */
.sect-head{display:flex;align-items:baseline;justify-content:space-between;gap:16px;margin:0 0 20px}
.sect-head h2{
  font-family:var(--serif);font-size:24px;font-weight:600;margin:0;letter-spacing:.01em;
  display:flex;align-items:center;gap:11px;
}
.sect-head h2::before{
  content:"";width:3px;height:19px;border-radius:2px;background:var(--accent);flex:0 0 3px;
}
.sect-head .more{font-size:12.5px;color:var(--muted);white-space:nowrap}
.sect-head .more:hover{color:var(--accent)}

/* 章节卡片 */
.cards{display:grid;grid-template-columns:repeat(auto-fill,minmax(238px,1fr));gap:14px;margin-bottom:46px}
.card{
  position:relative;overflow:hidden;
  background:var(--surface);border:1px solid var(--line);border-radius:var(--r);
  padding:20px 20px 18px;
  transition:transform .2s cubic-bezier(.2,.7,.3,1),box-shadow .24s,border-color .24s;
  display:flex;flex-direction:column;min-height:150px;
}
.card:hover{transform:translateY(-3px);box-shadow:var(--shadow-md);border-color:#DAD3C2}
.card .c-no{
  position:absolute;right:14px;top:6px;
  font-family:var(--serif);font-size:52px;line-height:1;
  color:#F1EDE2;font-weight:600;pointer-events:none;letter-spacing:-.03em;
}
.card h3{font-family:var(--serif);font-size:17.5px;margin:0 0 7px;font-weight:600;position:relative;z-index:1;letter-spacing:.01em;padding-right:46px}
.card .c-en{font-size:10px;letter-spacing:.1em;text-transform:uppercase;color:#B0A897;margin-bottom:10px;padding-right:38px;white-space:nowrap;overflow:hidden;text-overflow:ellipsis}
.card p{font-size:12.5px;line-height:1.7;color:var(--muted);margin:0 0 14px;position:relative;z-index:1;flex:1}
.card .c-foot{display:flex;align-items:center;justify-content:space-between;font-size:11px;color:#A39B8C;position:relative;z-index:1}
.card .stars{color:var(--seal);letter-spacing:1px}
.card.done{border-color:#CFE4D8;background:linear-gradient(180deg,#FCFEFC,var(--surface))}
.card.done .c-foot .ck{color:var(--green)}

/* 学习路线 */
.timeline{position:relative;margin:0 0 48px;padding-left:26px}
.timeline::before{content:"";position:absolute;left:5px;top:8px;bottom:8px;width:1.5px;background:linear-gradient(180deg,var(--accent),#CFC8B9 85%)}
.tl-item{position:relative;margin-bottom:26px}
.tl-item::before{
  content:"";position:absolute;left:-26px;top:5px;width:9px;height:9px;border-radius:50%;
  background:var(--paper);border:2px solid var(--accent);
}
.tl-item:last-child::before{border-color:#CFC8B9}
.tl-item h4{margin:0 0 6px;font-size:14.5px;font-weight:600;display:flex;gap:10px;align-items:baseline;flex-wrap:wrap}
.tl-item h4 .ph{font-family:var(--serif);font-size:11px;color:var(--accent);letter-spacing:.1em}
.tl-item p{margin:0;font-size:13px;line-height:1.75;color:var(--ink-2)}

/* ============ 章节页 ============ */
.ch-head{position:relative;margin-bottom:34px;padding-bottom:26px;border-bottom:1px solid var(--line)}
.ch-kicker{display:flex;align-items:center;gap:10px;font-size:11px;letter-spacing:.14em;text-transform:uppercase;color:var(--muted);margin-bottom:14px}
.ch-kicker .pill{
  padding:3px 9px;border-radius:99px;background:var(--accent-soft);color:var(--accent);
  font-weight:600;letter-spacing:.08em;
}
.ch-head h1{font-family:var(--serif);font-size:38px;line-height:1.2;margin:0 0 12px;font-weight:600;letter-spacing:-.01em}
.ch-head .ch-sub{font-size:14.5px;line-height:1.85;color:var(--ink-2);margin:0;max-width:640px}
.ch-tags{display:flex;gap:7px;flex-wrap:wrap;margin-top:16px}
.tag{font-size:11px;padding:4px 10px;border-radius:99px;background:var(--paper-2);color:var(--ink-2);border:1px solid var(--line)}
.done-btn{
  position:absolute;right:0;top:2px;
  display:inline-flex;align-items:center;gap:7px;
  font-size:12px;padding:8px 13px;border-radius:9px;
  border:1px solid var(--line);background:var(--surface);color:var(--ink-2);
  transition:all .18s;
}
.done-btn:hover{border-color:#CFE4D8;color:var(--green)}
.done-btn.on{background:var(--green-soft);border-color:#CFE4D8;color:var(--green);font-weight:600}

.sec{margin-bottom:44px}
.sec-h{display:flex;align-items:center;gap:11px;margin:0 0 18px}
.sec-h h2{font-family:var(--serif);font-size:21px;font-weight:600;margin:0;letter-spacing:.01em}
.sec-h .bar{width:3px;height:17px;border-radius:2px;background:var(--accent)}
.sec-h.alt .bar{background:var(--seal)}
.sec-h .count{font-size:11px;color:#A39B8C;margin-left:auto;font-variant-numeric:tabular-nums}

/* 概念 */
.concept{
  border-left:2px solid var(--line);
  padding:2px 0 2px 18px;margin-bottom:20px;
  transition:border-color .2s;
}
.concept:hover{border-left-color:var(--accent)}
.concept h3{font-size:14.5px;font-weight:600;margin:0 0 6px;display:flex;align-items:center;gap:8px}
.concept h3 .n{
  font-family:var(--serif);font-size:11px;color:var(--accent);
  width:18px;height:18px;border-radius:50%;background:var(--accent-soft);
  display:grid;place-items:center;flex:0 0 18px;font-weight:600;
}
.concept p{margin:0;font-size:13.5px;line-height:1.9;color:var(--ink-2)}

/* 公式 */
.fgrid{display:grid;grid-template-columns:repeat(auto-fill,minmax(300px,1fr));gap:12px}
.fitem{
  background:var(--surface);border:1px solid var(--line);border-radius:11px;
  padding:14px 16px;min-width:0;
}
.fitem .fl{font-size:11.5px;color:var(--muted);margin-bottom:8px;letter-spacing:.02em}
.fitem .fv{font-size:13.5px;overflow-x:auto;overflow-y:hidden;padding:2px 0 4px}
.fitem .fv .katex-display{margin:.28em 0;text-align:left}
.fitem .fv>div+div{margin-top:2px}
.fitem .fv::-webkit-scrollbar{height:5px}
.fitem .fv::-webkit-scrollbar-thumb{background:#E2DCCC;border-radius:9px}

/* 例题 */
.ex{
  background:var(--surface);border:1px solid var(--line);border-radius:var(--r);
  margin-bottom:14px;overflow:hidden;
}
.ex-q{padding:18px 20px 16px;display:flex;gap:12px;align-items:flex-start}
.ex-badge{
  flex:0 0 auto;font-family:var(--serif);font-size:11px;font-weight:600;
  color:var(--seal);background:var(--seal-soft);border-radius:6px;
  padding:3px 7px;margin-top:1px;letter-spacing:.05em;
}
.ex-q .txt{font-size:13.5px;line-height:1.9;color:var(--ink-2)}
.ex-toggle{
  font-size:12px;color:var(--accent);padding:0 20px 14px 58px;
  display:inline-flex;align-items:center;gap:6px;font-weight:600;
}
.ex-toggle .arw{transition:transform .22s;font-size:9px}
.ex.open .ex-toggle .arw{transform:rotate(90deg)}
.ex-sol{
  display:none;padding:16px 20px 18px 58px;
  background:linear-gradient(180deg,#FCFBF7,#FFFFFF);
  border-top:1px dashed var(--line);
  font-size:13.5px;line-height:2;color:var(--ink-2);
}
.ex.open .ex-sol{display:block;animation:fade .28s ease}
@keyframes fade{from{opacity:0;transform:translateY(-4px)}to{opacity:1;transform:none}}
.ex-sol .step{display:flex;gap:9px;margin-bottom:4px}
.ex-sol .step .s{
  flex:0 0 15px;font-family:var(--serif);font-size:11px;color:#A39B8C;
  padding-top:6px;font-variant-numeric:tabular-nums;
}

/* 易错点 */
.pit{
  display:grid;grid-template-columns:1fr 1fr;gap:0;
  border:1px solid var(--line);border-radius:11px;overflow:hidden;
  margin-bottom:12px;background:var(--surface);align-items:start;
}
.pit>div{padding:15px 18px;font-size:12.5px;line-height:1.85}
.pit .bad{background:#FDF7F5;border-right:1px solid var(--line);height:100%}
.pit .good{background:#F8FBF9;height:100%}
.pit .plab{font-size:10px;letter-spacing:.12em;font-weight:700;text-transform:uppercase;margin-bottom:7px;display:flex;align-items:center;gap:5px}
.pit .bad .lab{color:var(--seal)}
.pit .good .lab{color:var(--green)}
.pit p{margin:0;color:var(--ink-2)}

/* 页面底部导航 */
.pager{display:flex;gap:12px;margin-top:46px;padding-top:26px;border-top:1px solid var(--line)}
.pager a{
  flex:1;padding:14px 16px;border:1px solid var(--line);border-radius:11px;
  background:var(--surface);transition:all .18s;min-width:0;
}
.pager a:hover{border-color:#D5CDBA;box-shadow:var(--shadow-sm);transform:translateY(-1px)}
.pager .dir{font-size:10.5px;letter-spacing:.1em;color:#A39B8C;text-transform:uppercase;margin-bottom:4px}
.pager .t{font-size:13.5px;font-weight:600;white-space:nowrap;overflow:hidden;text-overflow:ellipsis}
.pager a.next{text-align:right}

/* ============ 公式速查 ============ */
.filter-row{display:flex;gap:8px;flex-wrap:wrap;margin-bottom:26px}
.chip{
  font-size:12px;padding:6px 13px;border-radius:99px;
  border:1px solid var(--line);background:var(--surface);color:var(--ink-2);
  transition:all .16s;
}
.chip:hover{border-color:#D5CDBA}
.chip.on{background:var(--ink);color:#FBF9F4;border-color:var(--ink);font-weight:600}
.fcat{margin-bottom:34px}
.fcat h2{
  font-family:var(--serif);font-size:18px;font-weight:600;margin:0 0 14px;
  display:flex;align-items:center;gap:9px;
}
.fcat h2 .ln{flex:1;height:1px;background:var(--line);margin-left:6px}
.frow{
  display:grid;grid-template-columns:200px minmax(0,1fr);gap:16px;
  padding:12px 0;border-bottom:1px dashed var(--line-2);align-items:center;
}
.frow:last-child{border-bottom:0}
.frow .fn{font-size:12.5px;color:var(--muted);line-height:1.6}
.frow .fx{font-size:14px;overflow-x:auto;padding:2px 0}
.frow .fx::-webkit-scrollbar{height:5px}
.frow .fx::-webkit-scrollbar-thumb{background:#E2DCCC;border-radius:9px}

/* ============ 学习路线页 ============ */
.phase{
  background:var(--surface);border:1px solid var(--line);border-radius:var(--r);
  padding:22px 24px;margin-bottom:16px;position:relative;overflow:hidden;
}
.phase .ph-badge{
  font-family:var(--sans);font-size:10.5px;letter-spacing:.1em;
  color:var(--accent);background:var(--accent-soft);
  padding:3px 9px;border-radius:99px;font-weight:600;flex:0 0 auto;
}
.phase h3{font-family:var(--serif);font-size:18px;margin:0 0 4px;font-weight:600;display:flex;align-items:center;gap:10px}
.phase .dur{font-size:11px;color:var(--accent);letter-spacing:.08em;font-weight:600;margin-bottom:12px}
.phase p{font-size:13.5px;line-height:1.85;color:var(--ink-2);margin:0 0 12px}
.phase ul{margin:0;padding-left:18px;font-size:13px;line-height:1.9;color:var(--ink-2)}
.phase ul li::marker{color:#C9C1B0}

/* ============ 自测 ============ */
.quiz-top{
  display:flex;align-items:center;gap:16px;flex-wrap:wrap;
  background:var(--surface);border:1px solid var(--line);border-radius:var(--r);
  padding:16px 20px;margin-bottom:24px;
}
.quiz-score{font-family:var(--serif);font-size:26px;font-weight:600;font-variant-numeric:tabular-nums}
.quiz-score small{font-size:12px;color:var(--muted);font-family:var(--sans);font-weight:400}
.quiz-top .bar{flex:1;height:6px;background:var(--paper-2);border-radius:99px;overflow:hidden;min-width:120px}
.quiz-top .bar i{display:block;height:100%;width:0;background:var(--accent);transition:width .4s}
.qitem{
  background:var(--surface);border:1px solid var(--line);border-radius:var(--r);
  padding:20px 22px;margin-bottom:14px;
}
.qitem .qh{font-size:13.5px;line-height:1.9;margin-bottom:14px;color:var(--ink)}
.qitem .qh .qn{font-family:var(--serif);color:var(--muted);margin-right:8px;font-variant-numeric:tabular-nums}
.opts{display:grid;gap:8px}
.opt{
  display:flex;gap:10px;align-items:flex-start;
  padding:10px 13px;border:1px solid var(--line);border-radius:9px;
  font-size:13px;line-height:1.7;color:var(--ink-2);text-align:left;
  transition:all .15s;background:#FDFCF9;
}
.opt:hover{border-color:#CFD6DB;background:var(--surface)}
.opt .k{
  flex:0 0 20px;height:20px;border-radius:50%;display:grid;place-items:center;
  font-size:11px;background:var(--paper-2);color:var(--muted);font-weight:600;margin-top:1px;
}
.opt.right{border-color:#BEDCCB;background:var(--green-soft);color:#1F5138}
.opt.right .k{background:#CFE7DA;color:#1F5138}
.opt.wrong{border-color:#EFCDC3;background:var(--seal-soft);color:#8B3421}
.opt.wrong .k{background:#F3D8CE;color:#8B3421}
.opt:disabled{cursor:default}
.qexp{
  margin-top:12px;padding:12px 14px;border-radius:9px;
  background:#F8F6F0;border:1px dashed var(--line);
  font-size:12.5px;line-height:1.85;color:var(--ink-2);display:none;
}
.qitem.answered .qexp{display:block}

/* ============ 函数实验室 ============ */
.lab{
  background:var(--surface);border:1px solid var(--line);border-radius:var(--r);
  padding:22px;margin-bottom:22px;
}
.lab-h{display:flex;align-items:baseline;justify-content:space-between;gap:14px;margin-bottom:6px;flex-wrap:wrap}
.lab-h h2{font-family:var(--serif);font-size:19px;margin:0;font-weight:600}
.lab-desc{font-size:12.5px;color:var(--muted);line-height:1.8;margin:0 0 16px}
.canvas-wrap{position:relative;width:100%;border:1px solid var(--line-2);border-radius:11px;overflow:hidden;background:#FDFCF8}
canvas{display:block;width:100%;height:326px;touch-action:none;cursor:crosshair}
.lab-ctrls{display:flex;gap:8px;flex-wrap:wrap;align-items:center;margin-top:14px}
.lab-ctrls .lbl{font-size:11.5px;color:var(--muted);margin-right:2px}
.readout{display:flex;gap:10px;flex-wrap:wrap;margin-top:14px}
.rd{
  flex:1;min-width:120px;background:#FBFAF6;border:1px solid var(--line-2);
  border-radius:9px;padding:10px 13px;
}
.rd .k{font-size:10.5px;color:var(--muted);letter-spacing:.06em;margin-bottom:4px}
.rd .v{font-family:var(--mono);font-size:15px;color:var(--ink);font-variant-numeric:tabular-nums}
.rd .v.acc{color:var(--accent)}
.rd .v.seal{color:var(--seal)}

input[type=range]{
  -webkit-appearance:none;appearance:none;height:4px;border-radius:99px;
  background:var(--line);outline:none;width:150px;
}
input[type=range]::-webkit-slider-thumb{
  -webkit-appearance:none;width:15px;height:15px;border-radius:50%;
  background:var(--surface);border:2px solid var(--accent);cursor:pointer;
  box-shadow:0 1px 4px rgba(0,0,0,.14);
}

/* ============ 搜索弹窗 ============ */
.modal{
  position:fixed;inset:0;z-index:100;display:none;
  background:rgba(27,31,36,.34);backdrop-filter:blur(3px);
  padding:12vh 20px 20px;
}
.modal.open{display:block;animation:veil .2s ease}
@keyframes veil{from{background:rgba(27,31,36,0)}to{background:rgba(27,31,36,.34)}}
.modal-card{
  max-width:620px;margin:0 auto;background:var(--surface);
  border-radius:16px;box-shadow:0 24px 70px rgba(20,24,28,.28);
  overflow:hidden;border:1px solid rgba(255,255,255,.5);
}
.modal-input{display:flex;align-items:center;gap:10px;padding:14px 16px;border-bottom:1px solid var(--line)}
.modal-input .st-icon{font-size:17px;color:#A39B8C}
.modal-input input{
  flex:1;border:0;outline:0;font-size:14.5px;font-family:inherit;
  background:transparent;color:var(--ink);
}
.modal-input input::placeholder{color:#A8A196}
.modal-results{max-height:52vh;overflow-y:auto;padding:8px}
.sr{
  display:flex;gap:12px;align-items:flex-start;padding:11px 13px;border-radius:10px;
  cursor:pointer;transition:background .12s;
}
.sr:hover,.sr.cursor{background:var(--paper-2)}
.sr .sr-k{
  flex:0 0 auto;font-size:10px;padding:3px 7px;border-radius:5px;
  background:var(--accent-soft);color:var(--accent);font-weight:600;margin-top:2px;letter-spacing:.03em;
}
.sr .sr-b{min-width:0}
.sr .sr-t{font-size:13.5px;font-weight:600;margin-bottom:3px;line-height:1.5}
.sr .sr-d{font-size:11.5px;color:var(--muted);line-height:1.6;overflow:hidden;display:-webkit-box;-webkit-line-clamp:2;-webkit-box-orient:vertical}
.sr mark{background:#FBEFC3;color:inherit;border-radius:2px;padding:0 1px}
.sr-empty{text-align:center;color:var(--muted);font-size:13px;padding:40px 20px;line-height:1.8}
.modal-hint{
  display:flex;gap:18px;padding:10px 18px;border-top:1px solid var(--line);
  font-size:11px;color:#A39B8C;background:#FCFBF7;
}
.modal-hint span{display:flex;align-items:center;gap:4px}

/* toast */
.toast{
  position:fixed;left:50%;bottom:34px;transform:translate(-50%,18px);
  background:var(--ink);color:#FBF9F4;font-size:12.5px;
  padding:10px 18px;border-radius:99px;opacity:0;pointer-events:none;
  transition:opacity .25s,transform .25s;z-index:200;
  box-shadow:0 8px 24px rgba(0,0,0,.2);
}
.toast.show{opacity:1;transform:translate(-50%,0)}

/* 页脚 */
.foot{padding:0 44px 46px;max-width:836px;margin:0 auto}
.foot p{font-size:11.5px;color:var(--muted);margin:0 0 4px;line-height:1.7}
.foot .foot-dim{color:#A8A196;font-size:11px}

/* KaTeX 微调 */
.katex{font-size:1.02em}
.katex-display{margin:.5em 0;overflow-x:auto;overflow-y:hidden;padding:2px 0}
.katex-display::-webkit-scrollbar{height:5px}
.katex-display::-webkit-scrollbar-thumb{background:#E2DCCC;border-radius:9px}

/* ============ 响应式 ============ */
@media (max-width:1180px){
  .main{grid-template-columns:minmax(0,1fr)}
  .toc{display:none}
}
@media (max-width:900px){
  .app{grid-template-columns:minmax(0,1fr)}
  .sidebar{
    position:fixed;left:0;top:0;width:276px;transform:translateX(-100%);
    transition:transform .28s cubic-bezier(.2,.7,.3,1);box-shadow:0 0 40px rgba(0,0,0,.15);
  }
  .sidebar.open{transform:none}
  .sidebar.open + .sidebar-scrim{display:block}
  .menu-btn{display:grid}
  .page{padding:32px 22px 30px}
  .hero{margin:0 0 32px;padding:40px 24px 34px;border-radius:16px}
  .foot{padding:0 22px 36px}
  .ch-head h1{font-size:30px}
  .done-btn{position:static;margin-top:16px}
  .pit{grid-template-columns:1fr}
  .pit .bad{border-right:0;border-bottom:1px solid var(--line)}
  .frow{grid-template-columns:1fr;gap:4px}
  .ex-sol{padding-left:20px}
  .ex-toggle{padding-left:20px}
}
@media (max-width:560px){
  .search-trigger span:not(.st-icon){display:none}
  .search-trigger kbd{display:none}
  .hero-meta{gap:22px}
  .cards{grid-template-columns:1fr}
  .pager{flex-direction:column}
}

@media print{
  .sidebar,.topbar,.toc,.pager,.foot{display:none}
  .app,.main{display:block;height:auto;overflow:visible}
  .scroller{overflow:visible}
  .ex-sol{display:block}
}