:root{
  --bg:#f3f5f9; --surface:#ffffff; --surface-2:#f7f9fc; --border:#e1e6ee;
  --text:#18212f; --muted:#5b6778; --faint:#8a95a6;
  --primary:#1f4e8c; --primary-600:#173e70; --primary-50:#e8f0fb;
  --success:#1d7a4f; --success-50:#e5f4ec; --warn:#b26a00;
  --radius:14px; --shadow:0 1px 2px rgba(16,24,40,.06),0 4px 16px rgba(16,24,40,.06);
  --font: system-ui,-apple-system,"Segoe UI",Roboto,"Helvetica Neue",Arial,sans-serif;
  --mono: ui-monospace,"SF Mono",Menlo,Consolas,monospace;
  --maxw: 1180px;
}
*{box-sizing:border-box}
html,body{margin:0;height:100%}
body{background:var(--bg);color:var(--text);font:16px/1.5 var(--font);-webkit-font-smoothing:antialiased;-webkit-text-size-adjust:100%}
[hidden]{display:none!important}
a{color:var(--primary)}
.mono{font-family:var(--mono);font-variant-numeric:tabular-nums}
.skip{position:absolute;left:-999px;top:0;background:#000;color:#fff;padding:8px 12px;z-index:10}
.skip:focus{left:8px}
:focus-visible{outline:3px solid #7aa7e8;outline-offset:2px}

/* Top bar */
.topbar{position:sticky;top:0;z-index:5;display:flex;align-items:center;justify-content:space-between;gap:12px;
  padding:10px max(16px,env(safe-area-inset-left));background:rgba(255,255,255,.92);backdrop-filter:saturate(1.4) blur(8px);border-bottom:1px solid var(--border)}
.brand{display:flex;align-items:center;gap:10px;text-decoration:none;color:var(--text);font-weight:650;letter-spacing:-.01em;min-width:0}
.brand-mark{width:28px;height:28px;border-radius:8px;flex:none;background:
  radial-gradient(circle at 50% 50%,transparent 9px,#fff 9px 11px,transparent 11px),linear-gradient(135deg,#1f4e8c,#2d7bb6)}
.brand-text{white-space:nowrap;overflow:hidden;text-overflow:ellipsis}
main{outline:none}
.view{max-width:var(--maxw);margin:0 auto;padding:24px 16px 48px}

/* Buttons */
.btn{white-space:nowrap;appearance:none;border:1px solid transparent;border-radius:10px;padding:11px 18px;font:600 15px/1.2 var(--font);cursor:pointer;
  display:inline-flex;align-items:center;justify-content:center;gap:8px;text-decoration:none;min-height:44px;transition:background .15s,border-color .15s,transform .05s}
.btn:active{transform:translateY(1px)}
.btn-primary{background:var(--primary);color:#fff}
.btn-primary:hover{background:var(--primary-600)}
.btn-secondary{background:var(--surface);color:var(--text);border-color:var(--border)}
.btn-secondary:hover{background:var(--surface-2);border-color:#cdd5e1}
.btn-success{background:var(--success);color:#fff}
.btn-success:hover{background:#166141}
.btn-ghost{background:transparent;color:var(--primary)}
.btn-ghost:hover{background:var(--primary-50)}
.btn-sm{padding:7px 12px;min-height:36px;font-size:14px}
.linkbtn{background:none;border:0;padding:0;color:var(--muted);text-decoration:underline;cursor:pointer;font:inherit}

/* TOC */
.toc-hero{padding:12px 0 20px}
.toc-hero h1{font-size:clamp(28px,4.2vw,40px);line-height:1.15;letter-spacing:-.02em;margin:0 0 6px}
.toc-sub{color:var(--muted);margin:0 0 16px}
.overall{display:flex;align-items:center;gap:14px;background:var(--surface);border:1px solid var(--border);border-radius:var(--radius);padding:14px 16px;box-shadow:var(--shadow);max-width:560px}
.overall .bar{flex:1}
.overall-label{font-size:14px;color:var(--muted);white-space:nowrap}
.bar{height:8px;border-radius:99px;background:#e6ebf2;overflow:hidden}
.bar>span{display:block;height:100%;background:linear-gradient(90deg,var(--primary),#2d7bb6);border-radius:99px;transition:width .3s}
.bar.done>span{background:var(--success)}

.topic-grid{list-style:none;margin:8px 0 0;padding:0;display:grid;grid-template-columns:repeat(auto-fill,minmax(270px,1fr));gap:16px}
.topic-card{position:relative;background:var(--surface);border:1px solid var(--border);border-radius:var(--radius);box-shadow:var(--shadow);overflow:hidden;display:flex;flex-direction:column;transition:transform .15s,box-shadow .15s,border-color .15s}
.topic-card:hover{transform:translateY(-2px);box-shadow:0 2px 4px rgba(16,24,40,.06),0 10px 24px rgba(16,24,40,.10);border-color:#cfd8e5}
.topic-thumb{display:block;aspect-ratio:4/3;background:#dfe5ee center/cover no-repeat;border-bottom:1px solid var(--border);position:relative}
.topic-thumb::after{content:"";position:absolute;inset:0;background:linear-gradient(180deg,transparent 55%,rgba(0,0,0,.05))}
.topic-accent{position:absolute;left:0;top:0;right:0;height:5px;z-index:1}
.topic-body{padding:14px 16px 16px;display:flex;flex-direction:column;gap:10px;flex:1}
.topic-name{font-size:19px;font-weight:700;letter-spacing:-.01em;margin:0;line-height:1.25}
.topic-name a{color:inherit;text-decoration:none}
.topic-name a::after{content:"";position:absolute;inset:0;z-index:1}  /* whole card clickable */
.topic-meta{color:var(--muted);font-size:14px;margin:0}
.topic-status{display:flex;align-items:center;justify-content:space-between;gap:8px;font-size:13.5px;color:var(--muted)}
.pill{display:inline-flex;align-items:center;gap:6px;padding:3px 10px;border-radius:99px;font-weight:600;font-size:12.5px;background:#eef1f6;color:var(--muted)}
.pill.inprogress{background:var(--primary-50);color:var(--primary)}
.pill.complete{background:var(--success-50);color:var(--success)}
.topic-actions{display:flex;gap:8px;margin-top:auto;position:relative;z-index:2}
.topic-actions .btn{flex:1;padding-left:12px;padding-right:12px}
.topic-status .pill,.topic-status>span:last-child{white-space:nowrap}
.toc-foot{color:var(--faint);font-size:13.5px;margin-top:28px;text-align:center}

/* Slide view */
#slideView{padding-top:14px;max-width:1100px}
.progress-panel{background:var(--surface);border:1px solid var(--border);border-radius:var(--radius);padding:12px 16px 14px;box-shadow:var(--shadow)}
.progress-row{display:flex;flex-wrap:wrap;align-items:baseline;justify-content:space-between;gap:6px 18px;margin-bottom:10px}
.topic-title{font-size:18px;margin:0;letter-spacing:-.01em}
.progress-stats{display:flex;flex-wrap:wrap;gap:4px 18px;font-size:14.5px;color:var(--muted)}
.progress-stats strong{color:var(--text);font-weight:650}
.segbar{display:flex;gap:3px;height:10px}
.seg{flex:1;min-width:0;border:0;padding:0;border-radius:3px;background:#e3e8f0;cursor:pointer;position:relative;transition:background .2s}
.seg:hover{background:#cdd6e3}
.seg.done{background:#8fc2a7}
.seg.done:hover{background:#79b394}
.seg.current{background:var(--primary);box-shadow:0 0 0 2px rgba(31,78,140,.25)}
.seg::before{content:"";position:absolute;left:0;right:0;top:-8px;bottom:-8px} /* bigger touch target */

.slide-frame{margin:14px 0 0;background:#fff;border:1px solid var(--border);border-radius:var(--radius);box-shadow:var(--shadow);overflow:hidden;position:relative;
  display:flex;align-items:center;justify-content:center}
.slide-frame img{display:block;width:100%;height:auto;max-height:calc(100vh - 318px);max-height:calc(100dvh - 318px);min-height:0;object-fit:contain;background:#fff}
.slide-loading{position:absolute;inset:auto 12px 12px auto;background:rgba(0,0,0,.6);color:#fff;font-size:13px;padding:4px 10px;border-radius:99px}

.player{margin-top:14px;display:flex;align-items:center;gap:10px;background:var(--surface);border:1px solid var(--border);border-radius:var(--radius);padding:10px 14px;box-shadow:var(--shadow)}
.play{flex:none;width:48px;height:48px;border-radius:50%;border:0;background:var(--primary);color:#fff;cursor:pointer;display:grid;place-items:center;transition:background .15s}
.play:hover{background:var(--primary-600)}
.play svg{width:24px;height:24px;fill:currentColor}
.play .i-pause{display:none}
.player.playing .play .i-play{display:none}
.player.playing .play .i-pause{display:block}
.player.loading .play{opacity:.75}
.skipbtn,.rate{flex:none;border:1px solid var(--border);background:var(--surface-2);color:var(--text);border-radius:8px;height:34px;padding:0 9px;font:600 13px/1 var(--font);cursor:pointer}
.skipbtn:hover,.rate:hover{background:#eef2f8}
.rate{min-width:48px}
.time{flex:none;font-size:14px;color:var(--muted);min-width:46px;text-align:center}
.seek-wrap{flex:1;min-width:60px;display:flex;align-items:center}
input[type=range]{--pct:0%;--buf:0%;width:100%;height:28px;background:transparent;-webkit-appearance:none;appearance:none;margin:0;cursor:pointer}
input[type=range]::-webkit-slider-runnable-track{height:6px;border-radius:99px;background:linear-gradient(90deg,var(--primary) var(--pct),#c9d3e1 var(--pct),#c9d3e1 var(--buf),#e3e8f0 var(--buf))}
input[type=range]::-moz-range-track{height:6px;border-radius:99px;background:linear-gradient(90deg,var(--primary) var(--pct),#c9d3e1 var(--pct),#c9d3e1 var(--buf),#e3e8f0 var(--buf))}
input[type=range]::-webkit-slider-thumb{-webkit-appearance:none;width:18px;height:18px;border-radius:50%;background:#fff;border:2px solid var(--primary);margin-top:-6px;box-shadow:0 1px 3px rgba(0,0,0,.2)}
input[type=range]::-moz-range-thumb{width:14px;height:14px;border-radius:50%;background:#fff;border:2px solid var(--primary);box-shadow:0 1px 3px rgba(0,0,0,.2)}
input[type=range]:disabled{cursor:default;opacity:.6}
.nav-mid{flex:1;display:flex;flex-direction:column;align-items:center;justify-content:center;gap:2px;font-size:13.5px;color:var(--muted);text-align:center;min-width:0}
.audio-status:empty{display:none}
.audio-status.error{color:#b42318}
.toggle{display:inline-flex;align-items:center;gap:6px;cursor:pointer;user-select:none}
.toggle input{width:16px;height:16px;accent-color:var(--primary)}

.slide-nav{display:flex;align-items:center;gap:12px;margin-top:12px}
.slide-nav .btn{min-width:140px}
.kbd-hint{color:var(--faint);font-size:12.5px;text-align:center;margin:14px 0 0}
kbd{font-family:var(--mono);font-size:11.5px;border:1px solid var(--border);border-bottom-width:2px;border-radius:5px;padding:1px 5px;background:#fff;color:var(--muted)}

/* Done */
.done-card{max-width:560px;margin:40px auto;text-align:center;background:var(--surface);border:1px solid var(--border);border-radius:18px;padding:36px 28px;box-shadow:var(--shadow)}
.done-badge{width:64px;height:64px;border-radius:50%;margin:0 auto 12px;background:var(--success-50);color:var(--success);display:grid;place-items:center;font-size:32px;font-weight:700}
.done-card h1{margin:0 0 8px;font-size:26px;letter-spacing:-.01em}
.done-card p{color:var(--muted);margin:0 0 22px}
.done-actions{display:flex;flex-direction:column;gap:10px;align-items:stretch;max-width:320px;margin:0 auto}
.noscript{text-align:center;padding:40px}

/* Mobile */
@media (max-width:720px){
  .view{padding:16px 12px 36px}
  #slideView{padding-top:10px}
  .progress-panel{padding:10px 12px 12px}
  .topic-title{font-size:16px}
  .progress-stats{font-size:13.5px}
  .slide-frame{margin-top:10px;border-radius:10px}
  .slide-frame img{max-height:none}
  .player{flex-wrap:wrap;gap:8px 10px;padding:10px 12px}
  .seek-wrap{order:10;flex-basis:100%}
  .time{min-width:auto}
  .player .time#durTime{margin-right:auto}
  .slide-nav{flex-wrap:wrap}
  .slide-nav .btn{min-width:0;flex:1}
  .nav-mid{order:-1;flex-basis:100%;align-items:flex-start;text-align:left;padding:0 2px}
  .topic-grid{grid-template-columns:1fr;gap:12px}
  .topic-card{display:grid;grid-template-columns:112px 1fr}
  .topic-thumb{aspect-ratio:auto;height:100%;min-height:100%;border-bottom:0;border-right:1px solid var(--border);background-color:#fff;background-size:contain;background-position:center}
  .topic-body{padding:12px 12px 12px;gap:8px}
  .topic-name{font-size:17px}
  .topic-actions .btn{min-height:40px;font-size:14px}
  .toc-hero h1{font-size:30px}
  .kbd-hint{display:none}
  .brand-text{font-size:15px}
}
@media (max-width:720px) and (orientation:landscape){
  .slide-frame img{max-height:calc(100dvh - 120px)}
}
@media (prefers-reduced-motion:reduce){*{transition:none!important}}