:root{
  --bg:#0d0f14; --bg2:#11141b; --panel:#161a23; --panel2:#1b2030;
  --border:#272d3a; --border2:#323a4d;
  --text:#e8ecf3; --muted:#98a2b3; --faint:#6b7280;
  --accent:#5eead4; --accent2:#fbbf24; --accent3:#7dd3fc;
  --danger:#f87171; --ok:#34d399;
  --shadow:0 10px 30px rgba(0,0,0,.45);
  --radius:14px;
  --maxw:880px;
  --font:"Segoe UI","PingFang SC","Microsoft YaHei",system-ui,-apple-system,sans-serif;
}
[data-theme="light"]{
  --bg:#f4f6fb; --bg2:#eef1f7; --panel:#ffffff; --panel2:#f7f9fc;
  --border:#e2e7f0; --border2:#d3dae6;
  --text:#1b2230; --muted:#5b6473; --faint:#8a93a3;
  --accent:#0d9488; --accent2:#b45309; --accent3:#0369a1;
  --shadow:0 10px 30px rgba(20,30,60,.12);
}
*{box-sizing:border-box}
html{scroll-behavior:smooth}
body{margin:0;font-family:var(--font);background:var(--bg);color:var(--text);
  line-height:1.75;font-size:16px;-webkit-font-smoothing:antialiased;}
a{color:var(--accent3);text-decoration:none}
::selection{background:var(--accent);color:#06241f}

/* ---------- topbar ---------- */
.topbar{position:sticky;top:0;z-index:50;display:flex;align-items:center;gap:14px;
  padding:12px 22px;background:rgba(13,15,20,.82);backdrop-filter:blur(12px);
  border-bottom:1px solid var(--border);}
[data-theme="light"] .topbar{background:rgba(255,255,255,.82)}
.brand{display:flex;align-items:center;gap:11px;font-weight:700;letter-spacing:.3px}
.brand .logo{width:30px;height:30px;border-radius:8px;display:grid;place-items:center;
  background:linear-gradient(135deg,var(--accent),var(--accent3));color:#06241f;font-weight:800}
.brand small{display:block;font-weight:400;color:var(--muted);font-size:11px;letter-spacing:1px}
.topbar .spacer{flex:1}
.btn{background:var(--panel);border:1px solid var(--border);color:var(--text);
  padding:8px 13px;border-radius:10px;cursor:pointer;font-size:13px;display:inline-flex;
  align-items:center;gap:7px;transition:.18s}
.btn:hover{border-color:var(--accent);color:var(--accent)}
.search-btn kbd{font-size:10px;border:1px solid var(--border2);border-radius:5px;padding:1px 5px;color:var(--muted)}
.progress-wrap{flex:0 0 200px;height:7px;background:var(--panel);border-radius:99px;overflow:hidden;border:1px solid var(--border)}
.progress-bar{height:100%;width:0;background:linear-gradient(90deg,var(--accent),var(--accent3));transition:width .3s}
.progress-label{font-size:12px;color:var(--muted);min-width:74px;text-align:right}

/* ---------- layout ---------- */
.layout{display:flex;align-items:flex-start;max-width:1400px;margin:0 auto}
.sidebar{position:sticky;top:62px;height:calc(100vh - 62px);width:300px;flex:0 0 300px;
  overflow-y:auto;padding:18px 12px 60px;border-right:1px solid var(--border);
  background:var(--bg2);scrollbar-width:thin}
.sidebar h4{margin:6px 10px 10px;font-size:12px;letter-spacing:1.5px;color:var(--faint);text-transform:uppercase}
.toc-chapter{margin-bottom:4px}
.toc-ch-title{display:flex;align-items:center;gap:9px;padding:9px 11px;border-radius:10px;cursor:pointer;
  font-weight:600;font-size:14.5px;transition:.15s;user-select:none}
.toc-ch-title:hover{background:var(--panel)}
.toc-ch-title .idx{width:22px;height:22px;border-radius:6px;display:grid;place-items:center;
  font-size:11px;background:var(--panel2);color:var(--accent);border:1px solid var(--border)}
.toc-ch-title .tag{margin-left:auto;font-size:10px;color:var(--muted);border:1px solid var(--border);
  padding:1px 7px;border-radius:99px}
.toc-ch-title .caret{transition:.2s;color:var(--muted);font-size:11px}
.toc-ch.collapsed .caret{transform:rotate(-90deg)}
.toc-ch.collapsed .toc-sections{display:none}
.toc-sections{margin:2px 0 6px 16px;padding-left:12px;border-left:1px solid var(--border)}
.toc-sec{display:flex;align-items:center;gap:8px;padding:6px 10px;border-radius:8px;cursor:pointer;
  font-size:13px;color:var(--muted);transition:.15s}
.toc-sec:hover{color:var(--text);background:var(--panel)}
.toc-sec.active{color:var(--accent);background:var(--panel2);font-weight:600}
.toc-sec .dot{width:7px;height:7px;border-radius:50%;background:var(--border2);flex:0 0 auto}
.toc-sec.done .dot{background:var(--ok);box-shadow:0 0 0 3px rgba(52,211,153,.18)}
.toc-progress{margin:4px 12px 14px;font-size:12px;color:var(--muted)}

/* ---------- content ---------- */
.content{flex:1;min-width:0;padding:0 30px 120px}
.hero{max-width:var(--maxw);margin:34px auto 10px;padding:30px;background:
  radial-gradient(1100px 380px at 80% -10%,rgba(94,234,212,.12),transparent),var(--panel);
  border:1px solid var(--border);border-radius:20px;box-shadow:var(--shadow)}
.hero h1{margin:0 0 6px;font-size:27px;letter-spacing:.5px}
.hero .sub{color:var(--muted);margin:0 0 18px}
.hero .pills{display:flex;flex-wrap:wrap;gap:9px;margin-bottom:20px}
.pill{font-size:12.5px;padding:5px 12px;border-radius:99px;border:1px solid var(--border2);
  background:var(--panel2);color:var(--text)}
.hero .map{display:flex;flex-wrap:wrap;gap:8px;align-items:center;margin-top:6px}
.map .node{padding:6px 12px;border-radius:9px;font-size:12.5px;border:1px solid var(--border2);
  background:var(--bg2);cursor:pointer;transition:.15s}
.map .node:hover{border-color:var(--accent);color:var(--accent)}
.map .arrow{color:var(--faint);font-size:13px}
.map .grp{border:1px dashed var(--border2);border-radius:12px;padding:8px 10px;display:flex;gap:7px;flex-wrap:wrap}
.map .grp .glabel{width:100%;font-size:11px;color:var(--faint);letter-spacing:1px;margin-bottom:2px}

.chapter{max-width:var(--maxw);margin:54px auto 0;scroll-margin-top:78px}
.ch-head{display:flex;align-items:flex-start;gap:16px;padding-bottom:16px;border-bottom:1px solid var(--border)}
.ch-head .num{font-size:40px;font-weight:800;line-height:1;color:transparent;
  -webkit-text-stroke:1.5px var(--accent);flex:0 0 auto}
.ch-head h2{margin:0;font-size:23px}
.ch-head .tag{display:inline-block;font-size:11px;color:var(--accent);border:1px solid var(--border2);
  padding:2px 9px;border-radius:99px;margin-bottom:8px}
.ch-head .sub2{color:var(--muted);margin:8px 0 0;font-size:14.5px}
.ch-intro{margin:18px 0;padding:16px 18px;background:var(--panel);border:1px solid var(--border);
  border-left:3px solid var(--accent);border-radius:12px;color:var(--text)}
.ch-intro b{color:var(--accent)}
.ch-keys{display:grid;grid-template-columns:1fr 1fr;gap:9px;margin:16px 0}
.key{font-size:13px;padding:9px 12px;background:var(--panel2);border:1px solid var(--border);
  border-radius:10px;color:var(--text)}
.key::before{content:"◆";color:var(--accent2);margin-right:8px;font-size:10px}
.src{font-size:12px;color:var(--faint);margin-top:14px;text-align:right}

/* sections */
.section{margin:34px 0;scroll-margin-top:78px}
.sec-head{display:flex;align-items:center;gap:11px;margin-bottom:12px}
.sec-head .snum{width:26px;height:26px;border-radius:8px;display:grid;place-items:center;
  background:var(--panel2);border:1px solid var(--border);font-size:12px;color:var(--accent);font-weight:700}
.sec-head h3{margin:0;font-size:18px}
.guide{background:var(--panel);border:1px solid var(--border);border-radius:12px;padding:15px 18px;margin:12px 0}
.guide .label{font-size:11px;letter-spacing:1.5px;color:var(--accent2);text-transform:uppercase;margin-bottom:6px;display:block}
.guide p{margin:0;color:var(--text)}

/* summary recap */
.summary{margin:14px 0;background:linear-gradient(90deg,rgba(99,179,237,.10),var(--panel));
  border:1px solid var(--border);border-left:3px solid var(--accent3);border-radius:12px;padding:14px 18px}
.summary .label{font-size:11px;letter-spacing:1.5px;color:var(--accent3);text-transform:uppercase;margin-bottom:6px;display:block}
.summary .summary-body{margin:0;color:var(--text);font-size:14.5px;line-height:1.85;white-space:pre-wrap}

/* figures */
.figures{display:flex;flex-direction:column;gap:14px;margin:14px 0}
figure.fig{margin:0;background:var(--panel);border:1px solid var(--border);border-radius:12px;
  overflow:hidden;cursor:zoom-in;transition:.18s}
figure.fig:hover{border-color:var(--accent)}
figure.fig img{width:100%;display:block;background:#fff}
[data-theme="light"] figure.fig img{background:#fff}
figure.fig figcaption{font-size:12.5px;color:var(--muted);padding:8px 13px;border-top:1px solid var(--border)}

/* tips callouts */
.tips{margin:14px 0;display:flex;flex-direction:column;gap:9px}
.tip{display:flex;gap:11px;padding:12px 15px;background:var(--panel2);border:1px solid var(--border);
  border-radius:11px;font-size:14px}
.tip .ic{flex:0 0 auto;width:22px;height:22px;border-radius:6px;background:var(--accent2);color:#3a2a02;
  display:grid;place-items:center;font-weight:800;font-size:13px}
.tip span{color:var(--text)}

/* raw text */
.raw{margin:12px 0}
.raw summary{cursor:pointer;font-size:13px;color:var(--accent3);padding:8px 12px;background:var(--panel2);
  border:1px solid var(--border);border-radius:10px;list-style:none;display:flex;align-items:center;gap:8px}
.raw summary::-webkit-details-marker{display:none}
.raw summary .chev{transition:.2s;color:var(--muted)}
.raw[open] summary .chev{transform:rotate(90deg)}
.raw .raw-body{margin-top:9px;padding:14px 16px;background:var(--bg2);border:1px solid var(--border);
  border-radius:10px;font-size:13.5px;color:var(--muted);white-space:pre-wrap;max-height:360px;overflow:auto;
  line-height:1.8;font-family:"Cascadia Code","Consolas",monospace}
.markdone{margin:18px 0 0;display:flex;align-items:center;gap:10px}
.markdone button{background:var(--panel);border:1px solid var(--border2);color:var(--text);
  padding:8px 14px;border-radius:10px;cursor:pointer;font-size:13px;transition:.15s}
.markdone button:hover{border-color:var(--ok);color:var(--ok)}
.markdone button.on{background:rgba(52,211,153,.12);border-color:var(--ok);color:var(--ok)}

/* ---------- lightbox ---------- */
.lightbox{position:fixed;inset:0;z-index:100;background:rgba(4,6,10,.92);display:none;
  align-items:center;justify-content:center;flex-direction:column;padding:30px}
.lightbox.show{display:flex}
.lightbox img{max-width:94vw;max-height:82vh;border-radius:8px;box-shadow:0 20px 60px rgba(0,0,0,.6);background:#fff}
.lightbox .lb-cap{color:#cfd6e2;margin-top:14px;font-size:13px}
.lightbox .lb-close{position:absolute;top:18px;right:22px;font-size:26px;color:#fff;cursor:pointer;
  background:none;border:none}
.lightbox .lb-nav{position:absolute;top:50%;transform:translateY(-50%);font-size:34px;color:#fff;
  cursor:pointer;background:rgba(255,255,255,.08);border:1px solid rgba(255,255,255,.15);
  width:52px;height:52px;border-radius:50%}
.lightbox .lb-prev{left:22px}.lightbox .lb-next{right:22px}

/* ---------- search modal ---------- */
.search-modal{position:fixed;inset:0;z-index:90;background:rgba(4,6,10,.7);display:none;
  align-items:flex-start;justify-content:center;padding-top:12vh}
.search-modal.show{display:flex}
.search-box{width:min(640px,92vw);background:var(--panel);border:1px solid var(--border2);
  border-radius:16px;box-shadow:var(--shadow);overflow:hidden}
.search-box input{width:100%;border:none;background:transparent;color:var(--text);
  padding:18px 20px;font-size:16px;outline:none;border-bottom:1px solid var(--border)}
.search-results{max-height:56vh;overflow:auto;padding:8px}
.sr-item{padding:11px 14px;border-radius:10px;cursor:pointer;transition:.12s}
.sr-item:hover{background:var(--panel2)}
.sr-item .t{font-weight:600;font-size:14px}
.sr-item .c{font-size:12px;color:var(--muted);margin-top:2px}
.sr-empty{padding:24px;text-align:center;color:var(--muted)}

/* back to top */
.totop{position:fixed;right:24px;bottom:24px;z-index:40;width:46px;height:46px;border-radius:50%;
  background:var(--panel);border:1px solid var(--border2);color:var(--accent);cursor:pointer;
  display:none;align-items:center;justify-content:center;font-size:20px;box-shadow:var(--shadow)}
.totop.show{display:flex}

/* mobile sidebar toggle */
.sb-toggle{display:none}
@media(max-width:980px){
  .sidebar{position:fixed;left:0;top:62px;z-index:45;transform:translateX(-100%);transition:.25s;
    width:280px;box-shadow:var(--shadow)}
  .sidebar.open{transform:translateX(0)}
  .sb-toggle{display:inline-flex}
  .content{padding:0 16px 100px}
  .ch-keys{grid-template-columns:1fr}
  .hero{padding:22px}
}