:root{
  --bg:#f6f7fb;--surface:#fff;--soft:#f1f3f9;--border:#e5e8f0;--text:#0f172a;--muted:#64748b;
  --accent:#4f46e5;--accent-h:#4338ca;--accent-soft:#eef0ff;--ok:#10b981;--danger:#ef4444;
  --r:14px;--shadow:0 1px 2px #0f172a0a,0 8px 24px -12px #0f172a1f;
}
@media(prefers-color-scheme:dark){:root{
  --bg:#0b0d13;--surface:#14171f;--soft:#1b1f2a;--border:#252a37;--text:#e9ecf3;--muted:#8a93a8;
  --accent:#7c83ff;--accent-h:#9298ff;--accent-soft:#1e2140;--shadow:0 1px 2px #0006,0 8px 24px -12px #000a;
}}
*{box-sizing:border-box}
html,body{height:100%}
body{margin:0;display:flex;flex-direction:column;height:100dvh;background:var(--bg);color:var(--text);
 font:15px/1.6 Inter,"Noto Sans TC","PingFang TC","Microsoft JhengHei",system-ui,sans-serif;-webkit-font-smoothing:antialiased}
button,select,input{font:inherit;color:inherit}
.ic{width:18px;height:18px;fill:none;stroke:currentColor;stroke-width:1.8;stroke-linecap:round;stroke-linejoin:round;flex:none}
button{cursor:pointer;display:inline-flex;align-items:center;justify-content:center;gap:6px;border:1px solid var(--border);border-radius:10px;padding:7px 12px;background:var(--surface);transition:background .15s,border-color .15s,color .15s}
button:hover{background:var(--soft)}
button:focus-visible,input:focus-visible,select:focus-visible{outline:2px solid var(--accent);outline-offset:2px}
button.primary{background:var(--accent);border-color:var(--accent);color:#fff;font-weight:600}
button.primary:hover{background:var(--accent-h)}
button.icon{width:40px;height:40px;padding:0;border-radius:10px}
button.icon.on{background:var(--accent-soft);border-color:var(--accent);color:var(--accent)}
#mic.on{background:var(--danger);border-color:var(--danger);color:#fff;animation:pulse 1.4s infinite}
@keyframes pulse{50%{box-shadow:0 0 0 6px #ef444430}}

/* start */
#start,#qr-modal{position:fixed;inset:0;z-index:10;display:flex;align-items:center;justify-content:center;padding:20px;background:var(--bg)}
#qr-modal{background:#0f172a99;backdrop-filter:blur(4px)}
#start[hidden],#qr-modal[hidden]{display:none}
.hero{max-width:460px;text-align:left}
.logo{font-weight:700;font-size:15px;letter-spacing:.02em;color:var(--accent);margin-bottom:28px;display:flex;align-items:center;gap:8px}
.logo::before{content:"";width:10px;height:10px;border-radius:50%;background:var(--accent)}
.hero h1{font-size:clamp(30px,6vw,42px);line-height:1.2;letter-spacing:-.02em;margin:0 0 14px}
.hero p{color:var(--muted);font-size:16px;margin:0 0 28px}
.hero small{display:block;margin-top:14px;color:var(--muted);font-size:13px}
button.lg{padding:12px 26px;font-size:16px;border-radius:12px}

/* header */
header{display:flex;align-items:center;gap:14px;padding:0 20px;height:60px;flex:none;background:var(--surface);border-bottom:1px solid var(--border)}
.brand{display:flex;align-items:center;gap:10px;margin-right:auto}
.title{display:flex;flex-direction:column;line-height:1.25}.title b{font-size:16px;letter-spacing:-.01em}
.title span{font-size:12px;color:var(--muted);display:flex;align-items:center;gap:6px}.title em{font-style:normal}
.dot{width:6px;height:6px;border-radius:50%;background:var(--ok)}
.chips{display:flex;gap:2px;padding:3px;background:var(--soft);border-radius:10px}
.chips button{border:0;background:transparent;padding:5px 12px;border-radius:8px;font-size:14px;color:var(--muted)}
.chips button:hover{color:var(--text);background:transparent}
.chips button.on{background:var(--surface);color:var(--text);box-shadow:0 1px 2px #0f172a1a}
select{height:40px;padding:0 10px;border-radius:10px;border:1px solid var(--border);background:var(--surface)}
.wave{display:flex;align-items:center;gap:2px;height:28px;width:28px;justify-content:center;flex:none;background:var(--accent-soft);border-radius:8px}
.wave i{display:block;width:3px;height:6px;border-radius:2px;background:var(--accent)}
.wave.speaking i{animation:eq .5s ease-in-out infinite alternate}
.wave.speaking i:nth-child(2){animation-delay:.12s}.wave.speaking i:nth-child(3){animation-delay:.24s}.wave.speaking i:nth-child(4){animation-delay:.06s}
@keyframes eq{from{height:5px}to{height:16px}}

/* layout */
main{flex:1;min-height:0;display:grid;grid-template-columns:minmax(0,1.55fr) minmax(320px,1fr);gap:16px;padding:16px 20px 20px;width:100%;max-width:1480px;margin:0 auto}
#board-wrap,#chat{background:var(--surface);border:1px solid var(--border);border-radius:var(--r);box-shadow:var(--shadow);min-height:0}
#board-wrap{position:relative;display:flex;align-items:center;justify-content:center;overflow:hidden;padding:12px}
#stage{position:relative;flex:none;width:100%;aspect-ratio:8/5}
#board{width:100%;height:100%;border-radius:8px;display:block}
.tag{position:absolute;top:12px;left:14px;font-size:12px;color:var(--muted);background:var(--soft);padding:2px 9px;border-radius:999px;z-index:1}
#board-hint{position:absolute;bottom:70px;color:#94a3b8;pointer-events:none;transition:opacity .4s;font-size:14px}

/* chat */
#chat{display:flex;flex-direction:column;overflow:hidden}
#log{flex:1;overflow-y:auto;padding:18px;display:flex;flex-direction:column;gap:10px;scroll-behavior:smooth}
.msg{padding:9px 14px;border-radius:14px;max-width:88%;white-space:pre-wrap;animation:in .2s ease-out}
@keyframes in{from{opacity:0;transform:translateY(4px)}}
.msg.angel{background:var(--soft);border-bottom-left-radius:4px;align-self:flex-start}
.msg.me{background:var(--accent);color:#fff;border-bottom-right-radius:4px;align-self:flex-end}
.msg img{max-width:180px;border-radius:8px;display:block;margin-top:6px}.msg.interim{opacity:.55}
#quick{display:flex;gap:6px;padding:4px 14px 10px;flex-wrap:wrap}
#quick button{border-radius:999px;font-size:13px;padding:5px 12px;color:var(--muted)}
#quick button:hover{color:var(--text)}#quick .ic{width:15px;height:15px}
#form{display:flex;gap:8px;padding:12px 14px;border-top:1px solid var(--border);align-items:center}
#form input{flex:1;height:40px;padding:0 14px;border-radius:10px;border:1px solid var(--border);min-width:0;background:var(--bg)}
#form input::placeholder{color:var(--muted)}

/* qr */
.card{background:var(--surface);border-radius:18px;padding:28px;max-width:380px;text-align:center;box-shadow:0 24px 60px #0f172a55}
.card h2{margin:0 0 4px;font-size:20px}.card p{margin:0 0 14px;color:var(--muted)}
#qr-modal img{width:220px;height:220px;border-radius:12px;border:1px solid var(--border);padding:8px;background:#fff}
#qr-url{font-size:11px;word-break:break-all;color:var(--muted);margin:10px 0 16px}

@media(max-width:860px){
  header{height:auto;flex-wrap:wrap;padding:10px 14px;gap:10px}.chips{order:5;width:100%;overflow-x:auto}.chips button{flex:1}
  main{grid-template-columns:1fr;grid-template-rows:auto minmax(0,1fr);padding:10px 12px 12px;gap:10px}
  #board-wrap{aspect-ratio:8/5}
}

button.danger{background:var(--danger);border-color:var(--danger);color:#fff}
button.danger:hover{background:#dc2626}
button[hidden]{display:none}

/* 深色白板 */
#board-wrap{background:#0f1720;border-color:#1f2a37}
#board-wrap .tag{background:#1b2634;color:#94a3b8}
#board-hint{color:#64748b}

#newchat{font-size:13px;color:var(--muted);height:40px}
#tray{display:flex;align-items:center;gap:8px;padding:8px 14px;border-top:1px solid var(--border);flex-wrap:wrap;background:var(--soft)}
#tray .th{position:relative}#tray img{height:46px;width:46px;object-fit:cover;border-radius:8px;border:1px solid var(--border);display:block}
#tray .th b{position:absolute;top:-6px;left:-6px;background:var(--accent);color:#fff;font-size:11px;min-width:18px;height:18px;border-radius:9px;display:flex;align-items:center;justify-content:center}
#tray span{font-size:13px;color:var(--muted);flex:1;min-width:140px}
#tray button{font-size:13px;padding:4px 10px}
.msg .ph{display:flex;gap:6px;flex-wrap:wrap;margin-top:6px}.msg .ph div{position:relative}
.msg .ph img{max-width:none;height:84px;width:auto;margin:0}
.msg .ph b{position:absolute;top:4px;left:4px;background:#0f172acc;color:#fff;font-size:11px;padding:0 6px;border-radius:6px}

#quick button.toggle.on{background:var(--accent-soft);border-color:var(--accent);color:var(--accent)}
.src{margin-top:8px;padding-top:6px;border-top:1px solid var(--border);font-size:12px;color:var(--muted);display:flex;flex-direction:column;gap:2px}
.src a{color:var(--accent);text-decoration:none;overflow:hidden;text-overflow:ellipsis;white-space:nowrap}.src a:hover{text-decoration:underline}

/* 白板上的公式層（KaTeX） */
#mathlayer{position:absolute;inset:0;pointer-events:none;overflow:hidden;border-radius:8px}
.mx{position:absolute;white-space:nowrap;font-size:calc(var(--s) * var(--u,1px));line-height:1.2;color:#f8fafc;
  clip-path:inset(0 100% 0 0);animation:wipe .7s ease-out forwards}
.mx .katex{font-size:1em}
@keyframes wipe{to{clip-path:inset(-20% -5% -20% -5%)}}
#sym{font-size:13px;width:auto;padding:0 10px;font-weight:600}
#sympad{display:grid;grid-template-columns:repeat(auto-fill,minmax(40px,1fr));gap:4px;padding:8px 14px;border-top:1px solid var(--border);background:var(--soft)}
#sympad[hidden]{display:none}
#sympad button{padding:4px 0;font-size:16px;border-radius:8px}
.msg .katex{font-size:1.05em}
[hidden]{display:none!important}
.heard{font-size:12px;color:var(--muted);margin-bottom:4px;padding-bottom:4px;border-bottom:1px dashed var(--border)}
.mx.pulse{animation:pz .9s ease-out}
@keyframes pz{40%{scale:1.2;filter:drop-shadow(0 0 12px #ffd43b)}}

/* 學生畫板（獨立彈出視窗，不與 Angel 的白板共用） */
#pad-modal{position:fixed;inset:0;z-index:12;display:flex;align-items:center;justify-content:center;padding:16px;background:#0f172a99;backdrop-filter:blur(4px)}
.padwin{display:flex;flex-direction:column;gap:10px;width:min(980px,100%);max-height:100%;padding:14px;border-radius:18px;background:var(--surface);border:1px solid var(--border);box-shadow:0 24px 60px #0f172a66}
.padbar{display:flex;align-items:center;gap:10px;flex-wrap:wrap}
.padbar b{font-size:16px;margin-right:auto}
#penopts{display:flex;align-items:center;gap:6px;flex-wrap:wrap}
#penopts .sw{width:28px;height:28px;padding:0;border-radius:50%;background:var(--c);border:2px solid var(--border);outline:0}
#penopts .sw.on{border-color:var(--text);box-shadow:0 0 0 2px var(--surface),0 0 0 4px var(--c)}
#penopts .tb{width:36px;height:36px;padding:0}#penopts .tb.on{background:var(--accent-soft);border-color:var(--accent);color:var(--accent)}
.padstage{align-self:center;width:100%;width:min(100%,calc((100vh - 190px) * 1.6));width:min(100%,calc((100dvh - 190px) * 1.6));aspect-ratio:8/5;border-radius:12px;overflow:hidden;background:#0f1720;border:1px solid #1f2a37}
#inkcv{display:block;width:100%;height:100%;touch-action:none;cursor:crosshair;
  background-image:radial-gradient(#223041 1.5px,transparent 1.5px);background-size:5% 8%}
.padfoot{display:flex;gap:8px}
.padfoot input{flex:1;height:40px;padding:0 14px;border-radius:10px;border:1px solid var(--border);background:var(--bg);min-width:0}

/* PWA */
body{padding:env(safe-area-inset-top) env(safe-area-inset-right) env(safe-area-inset-bottom) env(safe-area-inset-left)}
button.ghost{height:40px;font-size:13px;background:transparent;border:1px solid var(--border);margin-left:8px}
#start .hero #install{vertical-align:middle}

/* 內建相機 */
#cam-modal{position:fixed;inset:0;z-index:14;background:#000;display:flex}
.camwin{position:relative;flex:1;display:flex;align-items:center;justify-content:center;overflow:hidden}
#camvideo{width:100%;height:100%;object-fit:contain;background:#000}
#camvideo.front{transform:scaleX(-1)}
#camflash{position:absolute;inset:0;background:#fff;opacity:0;pointer-events:none;transition:opacity .15s}#camflash.on{opacity:.8;transition:none}
.camtop{position:absolute;top:max(14px,env(safe-area-inset-top));left:0;right:0;text-align:center}
.camtop span{display:inline-block;padding:6px 14px;border-radius:999px;background:#000a;color:#fff;font-size:14px}
#camerr{position:absolute;left:16px;right:16px;top:30%;padding:14px 16px;border-radius:12px;background:#000c;color:#fff;text-align:center;line-height:1.6}
.cambar{position:absolute;left:0;right:0;bottom:0;display:flex;align-items:center;justify-content:space-around;padding:16px 12px calc(16px + env(safe-area-inset-bottom));background:linear-gradient(transparent,#000b)}
.camside{display:flex;flex-direction:column;gap:8px;min-width:84px}
.cb{background:#ffffff22;color:#fff;border:0;border-radius:999px;padding:8px 14px;font-size:14px;backdrop-filter:blur(6px)}
.cb.done{background:var(--accent)}
.shutter{width:76px;height:76px;border-radius:50%;padding:0;border:4px solid #fff;background:#ffffff33;box-shadow:inset 0 0 0 5px #fff}
.shutter:disabled{opacity:.4}.shutter:active{transform:scale(.94)}