/* ============ 基础与变量 ============ */
:root{
  --ink:#2a2f3a; --ink-2:#5b6472; --ink-3:#8a93a3;
  --paper:#f7f6f3; --card:#ffffff; --line:#e4e1da;
  --brand:#2b4a9b; --brand-2:#4a6fd4; --brand-ink:#ffffff;
  --accent:#e8871e; --accent-soft:#fff4e5;
  --green:#2e7d32; --green-soft:#e9f5ea;
  --red:#c0392b; --red-soft:#fdecea;
  --indigo-soft:#eef1fb; --blue-soft:#e8f1fd;
  --amber-soft:#fdf3e0; --purple-soft:#f3eefa;
  --radius:14px; --radius-s:9px;
  --shadow:0 1px 2px rgba(20,25,40,.06),0 8px 24px -12px rgba(20,25,40,.14);
  --shadow-sm:0 1px 2px rgba(20,25,40,.06);
  --serif:"Songti SC","Noto Serif SC","Source Han Serif SC",SimSun,serif;
  --sans:-apple-system,BlinkMacSystemFont,"Segoe UI","PingFang SC","Hiragino Sans GB","Microsoft YaHei",sans-serif;
  --mono:"JetBrains Mono",Consolas,"Courier New",monospace;
}
*{box-sizing:border-box}
html{scroll-behavior:smooth}
body{margin:0;background:var(--paper);color:var(--ink);font-family:var(--sans);line-height:1.75;font-size:16px}
a{color:var(--brand);text-decoration:none}
a:hover{color:var(--brand-2)}
img{max-width:100%}
button{font-family:inherit;cursor:pointer}
::selection{background:#c9d6f7}

.app{min-height:100vh;display:flex;flex-direction:column}

/* ============ 顶栏 ============ */
.topbar{position:sticky;top:0;z-index:60;display:flex;align-items:center;gap:14px;
  background:linear-gradient(90deg,#243a75,#2b4a9b 55%,#3560c4);color:#fff;
  padding:0 18px;height:58px;box-shadow:0 2px 10px rgba(20,30,60,.25)}
.brand{color:#fff;font-weight:700;font-size:19px;letter-spacing:1px;white-space:nowrap}
.brand:hover{color:#fff}
.topbar-sub{font-size:12.5px;opacity:.85;white-space:nowrap;overflow:hidden;text-overflow:ellipsis}
.topbar-right{margin-left:auto;display:flex;align-items:center;gap:10px}
.icon-btn{background:rgba(255,255,255,.14);border:1px solid rgba(255,255,255,.25);color:#fff;
  border-radius:9px;width:38px;height:38px;font-size:18px;line-height:1;display:none;align-items:center;justify-content:center}
.ghost-btn{background:rgba(255,255,255,.12);color:#fff;border:1px solid rgba(255,255,255,.3);
  border-radius:9px;padding:6px 12px;font-size:13px}
.ghost-btn:hover{background:rgba(255,255,255,.22)}
.progress-badge{background:rgba(255,255,255,.16);border:1px solid rgba(255,255,255,.3);
  border-radius:20px;padding:4px 12px;font-size:13px;white-space:nowrap}

/* ============ 布局 ============ */
.layout{display:flex;flex:1;min-height:0}
.sidebar{width:300px;flex:0 0 300px;background:var(--card);border-right:1px solid var(--line);
  overflow-y:auto;position:sticky;top:58px;height:calc(100vh - 58px);padding:14px 10px 40px}
.main{flex:1;min-width:0;display:flex;flex-direction:column}
.view{flex:1;width:100%;max-width:1060px;margin:0 auto;padding:30px 34px 60px}
.site-footer{border-top:1px solid var(--line);background:#f1efe9;color:var(--ink-3);
  font-size:12.5px;padding:16px 24px;line-height:1.7;text-align:center}
.site-footer p{margin:2px 0}

/* ============ 侧边导航 ============ */
.side-nav{display:flex;flex-direction:column;gap:4px}
.side-nav h4{margin:14px 6px 6px;font-size:13px;color:var(--ink-3);letter-spacing:2px;font-weight:600}
.side-nav h4:first-child{margin-top:2px}
.nav-item{display:flex;align-items:baseline;gap:9px;padding:7px 10px;border-radius:9px;color:var(--ink-2);font-size:14.5px}
.nav-item:hover{background:#f0f2f7;color:var(--brand)}
.nav-item.active{background:var(--indigo-soft);color:var(--brand);font-weight:600}
.nav-item .no{font-family:var(--mono);font-size:12px;color:var(--ink-3);min-width:30px}
.nav-item.active .no{color:var(--brand)}
.nav-item .done{color:var(--green);font-size:12px}
.nav-home{font-weight:700;color:var(--ink)}

.backdrop{display:none;position:fixed;inset:0;background:rgba(20,25,40,.45);z-index:64}

/* ============ 通用组件 ============ */
.card{background:var(--card);border:1px solid var(--line);border-radius:var(--radius);box-shadow:var(--shadow-sm)}
.btn{display:inline-flex;align-items:center;gap:7px;background:var(--brand);color:#fff;border:none;
  border-radius:10px;padding:9px 16px;font-size:14.5px;font-weight:600;transition:filter .15s}
.btn:hover{filter:brightness(1.08);color:#fff}
.btn.ghost{background:#fff;color:var(--brand);border:1px solid var(--brand-2)}
.btn.soft{background:var(--indigo-soft);color:var(--brand)}
.btn.accent{background:var(--accent)}
.chip{display:inline-block;background:#eef0f5;color:var(--ink-2);border-radius:20px;
  padding:3px 12px;font-size:13px}
.chip.brand{background:var(--indigo-soft);color:var(--brand)}
.chip.green{background:var(--green-soft);color:var(--green)}
.katex{font-size:1.06em}
.katex-display{margin:14px 0;overflow-x:auto;overflow-y:hidden;padding:4px 2px}

/* ============ 首页 ============ */
.hero{background:linear-gradient(135deg,#243a75 0%,#2b4a9b 55%,#3f6bd8 100%);color:#fff;
  border-radius:20px;padding:40px 44px;position:relative;overflow:hidden;box-shadow:var(--shadow)}
.hero::after{content:"∑ ∫ ∂ √ ∞";position:absolute;right:-8px;bottom:-30px;font-size:120px;
  opacity:.08;font-family:var(--serif);letter-spacing:-6px}
.hero h1{margin:0 0 8px;font-size:34px;letter-spacing:1px}
.hero .sub{opacity:.92;font-size:16.5px;max-width:760px}
.hero .feats{display:flex;flex-wrap:wrap;gap:10px;margin-top:22px}
.hero .feats span{background:rgba(255,255,255,.14);border:1px solid rgba(255,255,255,.28);
  border-radius:20px;padding:6px 14px;font-size:13.5px}
.stats-row{display:flex;gap:14px;margin:22px 0 6px;flex-wrap:wrap}
.stat-card{flex:1;min-width:150px;background:var(--card);border:1px solid var(--line);
  border-radius:var(--radius);padding:16px 18px;box-shadow:var(--shadow-sm)}
.stat-card .num{font-size:28px;font-weight:800;color:var(--brand);line-height:1.2}
.stat-card .lbl{font-size:13px;color:var(--ink-2)}
.stat-bar{height:9px;background:#e6e3db;border-radius:20px;overflow:hidden;margin-top:8px}
.stat-bar i{display:block;height:100%;background:linear-gradient(90deg,var(--brand),var(--brand-2));border-radius:20px;transition:width .4s}

.home-block{margin-top:34px}
.home-block h2{font-size:21px;margin:0 0 4px;display:flex;align-items:center;gap:9px}
.home-block .hint{color:var(--ink-3);font-size:13.5px;margin:0 0 14px}
.vol-section{margin-bottom:30px}
.vol-head{display:flex;align-items:center;gap:12px;margin:26px 0 4px}
.vol-badge{background:var(--brand);color:#fff;border-radius:10px;padding:4px 13px;font-weight:700;font-size:15px}
.vol-badge.v2{background:#7a4fbf}
.vol-head .vd{color:var(--ink-2);font-size:14.5px}
.ch-grid{display:grid;grid-template-columns:repeat(auto-fill,minmax(250px,1fr));gap:14px;margin-top:14px}
.ch-card{display:flex;flex-direction:column;gap:8px;padding:16px 18px;background:var(--card);
  border:1px solid var(--line);border-radius:var(--radius);transition:transform .15s,box-shadow .15s,border-color .15s}
.ch-card:hover{transform:translateY(-3px);box-shadow:var(--shadow);border-color:#c9d4ef;color:var(--ink)}
.ch-card .ch-no{font-family:var(--mono);font-size:12px;color:var(--brand);font-weight:700;letter-spacing:1px}
.ch-card.v2 .ch-no{color:#7a4fbf}
.ch-card .ch-title{font-size:16.5px;font-weight:700;line-height:1.45}
.ch-card .ch-desc{font-size:13px;color:var(--ink-2);flex:1}
.ch-card .ch-meta{display:flex;gap:8px;align-items:center;font-size:12px;color:var(--ink-3)}
.ch-card.done{border-color:#bcd9c0}
.ch-card.done .ch-title::after{content:"✓ 已完成";float:right;font-size:11.5px;color:var(--green);font-weight:600}

/* ============ 章节视图 ============ */
.crumb{font-size:13px;color:var(--ink-3);margin-bottom:14px;display:flex;flex-wrap:wrap;gap:6px;align-items:center}
.ch-header{background:linear-gradient(135deg,#243a75,#2b4a9b 60%,#3f6bd8);color:#fff;
  border-radius:18px;padding:26px 30px;box-shadow:var(--shadow);position:relative;overflow:hidden}
.ch-header::after{content:attr(data-sym);position:absolute;right:14px;bottom:-26px;font-size:130px;opacity:.09;font-family:var(--serif)}
.ch-header .vol{font-size:13px;opacity:.85;letter-spacing:1px}
.ch-header h1{margin:4px 0 6px;font-size:26px}
.ch-header .en{font-size:14px;opacity:.75}
.ch-tagline{font-size:14.5px;opacity:.95;margin-top:6px;max-width:820px}
.ch-toc{display:flex;flex-wrap:wrap;gap:8px;margin:16px 0 4px}
.toc-chip{background:var(--card);border:1px solid var(--line);color:var(--ink-2);border-radius:20px;
  padding:5px 13px;font-size:13.5px;box-shadow:var(--shadow-sm)}
.toc-chip:hover{border-color:var(--brand-2);color:var(--brand)}
.ch-intro{background:var(--card);border:1px solid var(--line);border-left:5px solid var(--brand);
  border-radius:10px;padding:16px 20px;margin:20px 0 6px;box-shadow:var(--shadow-sm)}
.ch-intro h3{margin:0 0 6px;font-size:16px;color:var(--brand);display:flex;align-items:center;gap:7px}
.ch-intro p{margin:0 0 8px}
.ch-intro p:last-child{margin-bottom:0}

/* 小节 */
.sec{margin-top:42px;scroll-margin-top:80px}
.sec-head{border-bottom:2px solid var(--brand);padding-bottom:6px;margin-bottom:18px;display:flex;align-items:baseline;gap:12px}
.sec-head h2{margin:0;font-size:23px;letter-spacing:.5px}
.sec-head .sec-no{color:var(--brand);font-family:var(--mono);font-size:15px;font-weight:700}
.sec-sub{margin:-8px 0 16px;color:var(--ink-2);font-size:15px}

/* 内容块 */
.blk.plain{background:transparent;border:none;box-shadow:none;padding:0;border-left:none}
.blk.plain .blk-body{margin-top:0}
.blk{border-radius:12px;padding:15px 19px;margin:16px 0;border:1px solid var(--line);background:var(--card);
  box-shadow:var(--shadow-sm);overflow-x:auto}
.blk p{margin:6px 0}
.blk-title{font-weight:700;display:flex;align-items:baseline;gap:10px;flex-wrap:wrap;margin-bottom:4px}
.blk-tag{font-family:var(--mono);font-size:12.5px;font-weight:700;border-radius:7px;padding:1.5px 9px;white-space:nowrap}
.blk-body{margin-top:4px}
.blk-body ul,.blk-body ol{margin:6px 0;padding-left:22px}
.blk .src{font-size:12.5px;color:var(--ink-3);margin-top:6px}

.blk.def{background:#fff;border-left:4px solid #6478c8}
.blk.def .blk-tag{background:#e8ecf9;color:#3c4f9b}
.blk.thm{background:linear-gradient(180deg,#fff, #f7f9ff);border-left:4px solid #2f6f4f}
.blk.thm .blk-tag{background:#e2f1e8;color:#24613f}
.blk.prop,.blk.lemma,.blk.cor{background:#fff;border-left:4px solid #3f7fa3}
.blk.prop .blk-tag,.blk.lemma .blk-tag,.blk.cor .blk-tag{background:#e2eef7;color:#256083}
.blk.ex{background:var(--card);border-left:4px solid var(--accent)}
.blk.ex .blk-tag{background:var(--accent-soft);color:#a8630f}
.blk.note{border-left:4px solid #8a93a3;background:#fbfbfa}
.blk.note .blk-tag{background:#eceef2;color:#5b6472}
.blk.warn{background:var(--red-soft);border-left:4px solid var(--red)}
.blk.warn .blk-tag{background:#fbdcd7;color:#a13226}
.blk.quote{background:var(--amber-soft);border-left:4px solid var(--accent)}
.blk.quote .blk-tag{background:#f7e3bd;color:#94610c}
.blk.tip{background:var(--green-soft);border-left:4px solid var(--green)}
.blk.tip .blk-tag{background:#d5ebd8;color:#256b2a}

.ans-box{margin-top:10px;border-top:1px dashed #d9d4c9;padding-top:8px;font-size:14.5px}
.ans-toggle{background:none;border:1px solid var(--brand-2);color:var(--brand);border-radius:8px;
  padding:3px 11px;font-size:13px;margin-top:6px}
.ans-toggle:hover{background:var(--indigo-soft)}

/* 互动板块 */
.inter{margin:22px 0;background:linear-gradient(180deg,#fdfcff,#f7f6fd);
  border:1px solid #d9d3ef;border-radius:var(--radius);padding:16px 18px;box-shadow:var(--shadow-sm)}
.inter-head{display:flex;align-items:center;gap:9px;font-weight:700;color:#55418f;font-size:16px;margin-bottom:4px}
.inter-desc{color:var(--ink-2);font-size:14px;margin:2px 0 10px}
.inter canvas{width:100%;background:#fff;border:1px solid #e2ddf3;border-radius:10px;display:block}
.inter-note{font-size:13px;color:var(--ink-3);margin-top:8px;text-align:center;min-height:20px}
.controls{display:flex;flex-wrap:wrap;gap:10px 18px;align-items:center;margin-top:12px}
.ctl{display:flex;align-items:center;gap:8px;font-size:13.5px;color:var(--ink-2)}
.ctl label{min-width:34px;font-weight:600;color:var(--ink)}
.ctl input[type=range]{width:130px;accent-color:#6a55c9}
.ctl .val{font-family:var(--mono);color:#55418f;min-width:38px;text-align:right;font-size:13px}
.ctl select{padding:4px 8px;border-radius:7px;border:1px solid var(--line);background:#fff;font-size:13.5px}
.ctl button{border:1px solid #6a55c9;color:#55418f;background:#fff;border-radius:8px;padding:3px 12px;font-size:13px}
.ctl button:hover{background:#efeafa}
.inter-status{margin-top:10px;font-size:14px;min-height:22px;padding:7px 11px;border-radius:9px;background:#fff;border:1px solid #e6e2f3}

/* ============ 练习 ============ */
.exercise-zone{margin-top:50px;background:var(--card);border:1px solid var(--line);border-radius:var(--radius);box-shadow:var(--shadow)}
.exercise-zone .ez-head{display:flex;align-items:center;gap:12px;padding:18px 22px 6px}
.exercise-zone .ez-head h2{margin:0;font-size:21px}
.exercise-zone .ez-head .cnt{font-size:13px;color:var(--ink-3)}
.ez-body{padding:4px 22px 22px}
.q-item{border:1px solid var(--line);border-radius:12px;padding:15px 18px;margin:14px 0;background:#fff}
.q-item .q-no{font-family:var(--mono);color:var(--brand);font-weight:700;font-size:13.5px;margin-right:8px}
.q-item .q-text{display:inline;font-size:15.5px}
.q-options{display:flex;flex-wrap:wrap;gap:9px;margin-top:11px}
.q-opt{border:1px solid #cfd4e0;background:#fff;border-radius:9px;padding:6px 14px;font-size:14.5px;text-align:left;transition:all .12s}
.q-opt:hover{border-color:var(--brand-2);background:var(--indigo-soft)}
.q-opt.correct{background:var(--green-soft);border-color:var(--green);color:var(--green);font-weight:600}
.q-opt.wrong{background:var(--red-soft);border-color:var(--red);color:var(--red)}
.q-opt:disabled{cursor:default;opacity:.95}
.q-feedback{margin-top:10px;font-size:14.5px;padding:8px 12px;border-radius:9px;display:none}
.q-feedback.show{display:block}
.q-feedback.ok{background:var(--green-soft);color:#1f5e25}
.q-feedback.bad{background:var(--red-soft);color:#8e2c20}
.q-actions{margin-top:9px;display:flex;gap:9px;align-items:center;flex-wrap:wrap}
.q-calc-ans{display:none;margin-top:9px;background:#f7f8fa;border:1px dashed #cfd4e0;border-radius:9px;padding:10px 13px;font-size:14.5px}
.q-calc-ans.show{display:block}
.q-hint{font-size:13px;color:var(--ink-3);font-style:italic}
.q-badge{display:inline-block;background:#eef0f5;border-radius:7px;padding:0 8px;font-size:12px;color:var(--ink-2);margin-right:8px;vertical-align:2px}
.ez-score{margin-top:16px;text-align:center;color:var(--ink-2);font-size:14.5px}

.ch-nav{display:flex;justify-content:space-between;gap:12px;margin-top:52px;flex-wrap:wrap}
.ch-nav .btn{max-width:320px;text-align:left;line-height:1.35}
.ch-nav .btn small{display:block;font-weight:400;opacity:.8;font-size:12px}
.mark-zone{margin-top:26px;text-align:center}

/* 响应式 */
@media (max-width:960px){
  .sidebar{position:fixed;left:0;top:58px;bottom:0;z-index:70;transform:translateX(-105%);transition:transform .25s;box-shadow:0 0 40px rgba(0,0,0,.2);height:auto}
  .sidebar.open{transform:none}
  .icon-btn{display:inline-flex}
  .backdrop.show{display:block}
  .view{padding:20px 16px 50px}
  .hero{padding:28px 24px}
  .topbar-sub{display:none}
}
@media (max-width:560px){
  .ch-grid{grid-template-columns:1fr}
  .stat-card{min-width:100%}
  .hero h1{font-size:26px}
  .topbar .progress-badge{display:none}
}