:root{
  --bg:#F3F4F6; --card:#fff; --soft:#E8E9ED; --line:#ECEDF0;
  --text:#1B1D21; --muted:#686C74; --ink:#17181C; --red:#B3261E;
  --lift:0 1px 2px rgba(20,22,28,.04),0 10px 26px rgba(20,22,28,.05);
  --sans:"PingFang SC","HarmonyOS Sans SC","MiSans","Noto Sans SC","Microsoft YaHei",system-ui,sans-serif;
}
*{box-sizing:border-box;-webkit-tap-highlight-color:transparent}
html,body{margin:0;height:100%}
body{background:var(--bg);color:var(--text);font:15px/1.6 var(--sans);-webkit-text-size-adjust:100%;display:flex;flex-direction:column;height:100dvh;overflow:hidden}
.top{display:flex;align-items:center;gap:10px;padding:11px 16px 8px;flex:none}
.top h1{font-size:16px;font-weight:500;margin:0}
.top .tag{font-size:11.5px;color:var(--muted);background:var(--soft);border-radius:20px;padding:2px 9px}
.top .grow{flex:1}
.icon-btn{width:34px;height:34px;min-height:34px;padding:0;border-radius:50%;border:0;background:var(--card);box-shadow:var(--lift);cursor:pointer;font-size:15px}
button{font:inherit;font-size:14px;min-height:38px;padding:0 14px;border:0;border-radius:19px;background:var(--card);color:var(--text);box-shadow:inset 0 0 0 1px #DDDFE4;cursor:pointer}
button.primary{background:var(--ink);color:#fff;box-shadow:none}
button:disabled{opacity:.4;cursor:default}
:focus-visible{outline:2px solid var(--ink);outline-offset:2px}
input,textarea,select{font:inherit;width:100%;border:0;border-radius:14px;padding:10px 13px;background:var(--card);box-shadow:inset 0 0 0 1px #DDDFE4;color:var(--text)}
input:focus,textarea:focus{outline:0;box-shadow:inset 0 0 0 1.5px var(--ink)}
textarea{resize:none;line-height:1.5}
label.f{display:block;font-size:13px;color:var(--muted);margin:14px 0 6px}
.hint{font-size:12.5px;color:var(--muted)}

/* 黑板 */
.stage{flex:1;min-height:0;padding:0 12px;display:flex}
.board{flex:1;min-height:0;background:var(--ink);border-radius:20px;padding:16px 16px 20px;overflow-y:auto;overflow-x:hidden;color:#F1F1EF;box-shadow:0 14px 32px rgba(20,22,28,.2);position:relative;scroll-behavior:smooth}
.board::-webkit-scrollbar{width:6px}
.board::-webkit-scrollbar-thumb{background:rgba(255,255,255,.16);border-radius:3px}
.board .prob{font-size:15px;line-height:1.75;color:#E9E9E6;padding-bottom:12px;border-bottom:1px dashed rgba(255,255,255,.14);margin-bottom:14px;white-space:pre-wrap}
.board .prob:empty{display:none}
.lines{display:flex;flex-direction:column;gap:6px}
.ln{font-size:15px;line-height:1.7;animation:fade .28s ease both;overflow-wrap:anywhere}
.ln.box{display:inline-block;align-self:flex-start;padding:9px 14px;border:1px solid rgba(255,255,255,.42);border-radius:10px;margin:6px 0;font-size:16px}
.ln.muted{color:#A8ABB2;font-size:13.5px}
.plotwrap{margin:8px 0 2px}
.figbox{background:rgba(255,255,255,.035);border-radius:12px;padding:6px 4px}
.figbox{display:flex;justify-content:center}
.figbox svg{display:block;width:100%;max-width:400px}
.plerr{color:#E8A0A0;font-size:12.5px}
.gap{height:12px;flex:none}
.waitspot{display:flex;align-items:center;gap:10px;margin:14px 0 4px;padding:11px 14px;border:1px dashed rgba(138,182,255,.5);border-radius:12px;background:rgba(138,182,255,.07);animation:fade .3s ease both}
.waitspot[hidden]{display:none!important}
.waitspot span{flex:1;font-size:13px;color:#A9C4F0}
.waitspot button{min-height:32px;padding:0 14px;font-size:13px;border-radius:16px;background:#8AB6FF;color:#0F1219;box-shadow:none;font-weight:500}
@keyframes fade{from{opacity:0;transform:translateY(5px)}to{opacity:1;transform:none}}
.board .katex{color:#F4F4F1;font-size:1.02em}
.board .katex-display{margin:0}
.caret{display:inline-block;width:2px;height:1em;background:#8AB6FF;vertical-align:-2px;animation:blink 1s steps(2) infinite}
@keyframes blink{50%{opacity:0}}

/* 状态条 */
.bar{flex:none;display:flex;align-items:center;gap:6px;padding:9px 16px 4px}
.pill{font-size:12px;color:var(--muted);background:var(--card);border-radius:14px;padding:4px 10px;box-shadow:var(--lift);white-space:nowrap;overflow:hidden;text-overflow:ellipsis;max-width:52%}
.pill.on{color:var(--ink);font-weight:500}
.bar .grow{flex:1}
.bar button{min-height:34px;padding:0 12px;font-size:13px;border-radius:17px}

/* 输入 */
.composer{flex:none;padding:8px 12px 10px;display:flex;gap:7px;align-items:flex-end}
.composer textarea{flex:1;min-height:44px;max-height:120px;padding:11px 14px;border-radius:22px;box-shadow:0 1px 2px rgba(20,22,28,.06),0 6px 18px rgba(20,22,28,.06)}
.composer button{border-radius:22px;padding:0 16px;height:44px;min-height:44px;flex:none}

/* 导航 */
.tabs{flex:none;display:flex;gap:2px;margin:0 12px 10px;padding:4px;border-radius:24px;background:rgba(255,255,255,.94);box-shadow:0 1px 2px rgba(20,22,28,.06),0 10px 24px rgba(20,22,28,.12)}
.tabs button{flex:1;min-width:0;height:42px;min-height:42px;padding:0;border-radius:21px;background:none;box-shadow:none;color:var(--muted);font-size:12.5px}
.tabs button[aria-current=page]{background:var(--ink);color:#fff}

/* 页面 */
.page{flex:1;min-height:0;overflow-y:auto;padding:0 16px 20px}
.card{background:var(--card);border-radius:16px;padding:14px;box-shadow:var(--lift);margin-top:10px}
.list .it{display:flex;gap:10px;align-items:flex-start;padding:12px 0;border-top:1px solid var(--line)}
.list .it:first-child{border-top:0}
.list .it .tx{flex:1;min-width:0;font-size:14px;line-height:1.55;white-space:pre-wrap;overflow-wrap:anywhere}
.list .it .meta{font-size:11.5px;color:var(--muted);margin-bottom:3px}
.list .it button{min-height:28px;padding:0 10px;font-size:12px;border-radius:14px;box-shadow:none;color:var(--muted);background:var(--soft);flex:none}
.list .it .katex{font-size:1em}
.empty{text-align:center;color:var(--muted);font-size:13px;padding:26px 0}
.sheet{position:fixed;inset:0;z-index:60;display:flex;align-items:flex-end;justify-content:center;background:rgba(20,22,28,.4)}
.sheet[hidden]{display:none}
.sheet .panel{width:100%;max-width:560px;background:var(--bg);border-radius:22px 22px 0 0;padding:18px 20px calc(22px + env(safe-area-inset-bottom));max-height:88vh;overflow:auto}
.sheet .bar2{display:flex;align-items:center;justify-content:space-between;margin-bottom:4px}
.sheet h2{font-size:17px;margin:0;font-weight:500}
.toast{position:fixed;left:50%;bottom:96px;transform:translateX(-50%);background:rgba(20,22,28,.9);color:#fff;font-size:13px;padding:9px 16px;border-radius:20px;z-index:80;opacity:0;transition:.2s;pointer-events:none;max-width:80vw;text-align:center}
.toast.on{opacity:1}
.hide{display:none!important}
@media(min-width:820px){.stage{padding:0 24px}.board{padding:22px 26px}.composer{padding:10px 24px 12px}.tabs{margin:0 24px 12px;max-width:560px;align-self:center;width:calc(100% - 48px)}.page{max-width:760px;width:100%;margin:0 auto}}



/* 选项按钮（问卷、画像） */
.opts{display:flex;flex-direction:column;gap:8px}
.opts.row{flex-direction:row;flex-wrap:wrap}
.opt{display:inline-flex;align-items:center;justify-content:center;height:auto;min-height:40px;padding:9px 15px;border-radius:14px;font-size:13.5px;text-align:center}
.opt[aria-pressed=true]{background:var(--ink);color:#fff;box-shadow:none}

.subjects{display:flex;gap:6px;overflow-x:auto;flex-wrap:nowrap;margin:12px 2px 0;padding-bottom:6px;scrollbar-width:none}
.subjects::-webkit-scrollbar{display:none}
.subjects .opt{flex:none}



.sayline{color:#9AA2AE;font-size:13px;line-height:1.55;margin:2px 0 8px;padding-left:2px;border-left:2px solid rgba(255,255,255,.12);padding-left:10px}


/* ========== 视觉细化 ========== */
.top .brand{display:flex;align-items:center;gap:8px}
.top .logo{width:26px;height:26px;border-radius:8px;background:var(--ink);color:#fff;display:grid;place-items:center;font-size:15px;font-weight:600;font-family:"Times New Roman",Georgia,serif;line-height:1}
.top .name{font-size:15px;font-weight:500;letter-spacing:.01em}
.top .stat{font-size:12px;color:var(--muted);white-space:nowrap}
.top .icon-btn svg{width:17px;height:17px;fill:none;stroke:currentColor;stroke-width:1.7;stroke-linecap:round;stroke-linejoin:round;display:block;margin:0 auto}

.tabs button{flex-direction:column;gap:3px;font-size:11px;padding:7px 0;line-height:1.1}
.tabs button svg{width:19px;height:19px;fill:none;stroke:currentColor;stroke-width:1.7;stroke-linecap:round;stroke-linejoin:round}
.tabs button[aria-current=page] svg{stroke-width:1.9}

.bar button{display:inline-flex;align-items:center;gap:5px}
.bar button svg{width:15px;height:15px;fill:none;stroke:currentColor;stroke-width:1.8;stroke-linecap:round;stroke-linejoin:round;flex:none}

/* 黑板空状态 */
.board{display:flex;flex-direction:column}
.lines{flex:0 0 auto}
.board-empty{flex:1;display:flex;flex-direction:column;align-items:center;justify-content:center;gap:9px;padding:26px 20px;text-align:center;min-height:240px}
.board-empty[hidden]{display:none!important}
.be-icon{width:62px;height:62px;color:#4A525E;margin-bottom:2px}
.be-title{font-size:15.5px;color:#D3D6DB;font-weight:500}
.be-sub{font-size:13px;color:#7C848E;max-width:250px;line-height:1.65}
.be-btn{margin-top:10px;min-height:40px;padding:0 24px;background:#F6F6F4;color:var(--ink);font-weight:500;border-radius:20px}

@media(min-width:900px){
  .stage{max-width:1000px;margin:0 auto;width:100%}
  .bar,.composer{max-width:1000px;margin-left:auto;margin-right:auto;width:100%}
  .tabs{max-width:520px;margin:0 auto 12px}
}

/* 修正：优先级与黑板高度 */
.stage{align-items:stretch}
.board{max-height:calc(100dvh - 210px)}
button.be-btn{background:#F6F6F4;color:var(--ink);box-shadow:none;font-weight:500;padding:0 26px;min-height:42px}
button.be-btn:hover{background:#fff}
.board-empty{justify-content:center;padding-top:20px}


/* 接着上次 */
.resume-card{display:flex;flex-direction:column;align-items:flex-start;gap:3px;width:100%;max-width:290px;margin-top:10px;padding:12px 14px;border-radius:14px;background:rgba(255,255,255,.06);border:1px solid rgba(255,255,255,.13);text-align:left;box-shadow:none}
.resume-card:hover{background:rgba(255,255,255,.1)}
.resume-card[hidden]{display:none!important}
.rc-lab{font-size:11.5px;color:#8A919B}
.rc-title{font-size:13.5px;color:#E4E6EA;line-height:1.45;display:-webkit-box;-webkit-line-clamp:2;-webkit-box-orient:vertical;overflow:hidden}

/* 题干固定在黑板顶部，滚板书时不跟着走 */
.board .prob{position:sticky;top:0;z-index:3;background:var(--ink);margin:-16px -16px 14px;padding:16px 16px 12px;border-bottom:1px dashed rgba(255,255,255,.14)}
.board .prob:empty{display:none}

/* 按下反馈 */
button{transition:transform .12s ease, background .16s ease, box-shadow .16s ease}
button:active:not(:disabled){transform:scale(.975)}
.card{transition:box-shadow .18s ease}
.tabs button:active{transform:none}

/* 空状态 */
.empty{display:flex;flex-direction:column;align-items:center;gap:6px;padding:38px 20px}
.em-ic{width:34px;height:34px;fill:none;stroke:#B8BEC8;stroke-width:1.6;stroke-linecap:round;stroke-linejoin:round;opacity:.55;margin-bottom:4px}
.em-t{font-size:13.5px;color:var(--muted);font-weight:500}
.em-s{font-size:12.5px;color:#A0A6AF;max-width:230px;line-height:1.6}

/* 会话切换 */
.conv-btn{display:inline-flex;align-items:center;gap:5px;max-width:150px;min-height:32px;padding:0 10px;border-radius:16px;background:var(--card);box-shadow:inset 0 0 0 1px #DDDFE4;font-size:12.5px;color:var(--muted)}
.conv-btn span{overflow:hidden;text-overflow:ellipsis;white-space:nowrap}
.conv-btn svg{width:13px;height:13px;fill:none;stroke:currentColor;stroke-width:2;stroke-linecap:round;stroke-linejoin:round;flex:none}
.conv-btn[hidden]{display:none!important}

/* 回到题目 */
.to-top{position:absolute;right:12px;bottom:12px;width:34px;height:34px;min-height:34px;padding:0;border-radius:50%;background:rgba(255,255,255,.9);box-shadow:0 4px 14px rgba(0,0,0,.35);display:grid;place-items:center;z-index:5}
.to-top[hidden]{display:none!important}
.to-top svg{width:16px;height:16px;fill:none;stroke:#17181C;stroke-width:2;stroke-linecap:round;stroke-linejoin:round}

/* 回放分页 */
.playnav{display:flex;align-items:center;justify-content:center;gap:12px;margin-top:10px}
.playnav button{min-height:34px;padding:0 14px;font-size:13px;border-radius:17px}
.playnav span{font-size:12.5px;color:var(--muted);min-width:52px;text-align:center}


/* 麦克风 */
.mic{width:44px;height:44px;min-height:44px;padding:0;border-radius:50%;flex:none;display:grid;place-items:center;background:var(--card);box-shadow:var(--lift)}
.mic svg{width:19px;height:19px;fill:none;stroke:#5A6068;stroke-width:1.8;stroke-linecap:round;stroke-linejoin:round}
.mic.on{background:#E85D5D;box-shadow:0 0 0 4px rgba(232,93,93,.18)}
.mic.on svg{stroke:#fff}
@keyframes micpulse{0%,100%{transform:scale(1)}50%{transform:scale(1.06)}}
.mic.on{animation:micpulse 1.1s ease-in-out infinite}

/* 标注层 */
.pen-layer{position:absolute;inset:0;width:100%;height:100%;z-index:4;pointer-events:none}
.pen-layer.on{pointer-events:auto;cursor:crosshair;touch-action:none}
#btnPen.active{background:#E8C46A;box-shadow:none;color:#17181C}
.bar button svg{pointer-events:none}

/* 长题折叠 */
.qbody.collapsed{max-height:4.4em;overflow:hidden;position:relative;-webkit-mask-image:linear-gradient(#000 55%,transparent)}

/* ========== 深色模式 ========== */
html[data-theme=dark]{
  --bg:#0F1218; --card:#181C24; --soft:#232A35; --line:#242B36;
  --text:#E6E9ED; --muted:#99A1AC;
}
html[data-theme=dark] body{background:var(--bg);color:var(--text)}
html[data-theme=dark] .card{background:var(--card);box-shadow:0 1px 2px rgba(0,0,0,.3)}
html[data-theme=dark] .tabs{background:rgba(24,28,36,.96);box-shadow:0 1px 2px rgba(0,0,0,.3),0 10px 24px rgba(0,0,0,.4)}
html[data-theme=dark] .tabs button[aria-current=page]{background:#E8EBF0;color:#12151B}
html[data-theme=dark] button{background:#1B2028;color:#E6E9ED;box-shadow:inset 0 0 0 1px #2A3140}
html[data-theme=dark] button.primary{background:#E8EBF0;color:#12151B;box-shadow:none}
html[data-theme=dark] .opt[aria-pressed=true]{background:#E8EBF0;color:#12151B}
html[data-theme=dark] input,html[data-theme=dark] textarea{background:#1B2028;color:#E6E9ED;box-shadow:inset 0 0 0 1px #2A3140}
html[data-theme=dark] .conv-btn{background:#1B2028;box-shadow:inset 0 0 0 1px #2A3140}
html[data-theme=dark] .icon-btn{background:#1B2028;box-shadow:inset 0 0 0 1px #2A3140}
html[data-theme=dark] .sheet .panel{background:#12151B}
html[data-theme=dark] .logo{background:#E8EBF0;color:#12151B}
html[data-theme=dark] .hint{color:#8D95A0}
html[data-theme=dark] .pill{background:#1B2028;box-shadow:inset 0 0 0 1px #2A3140}
html[data-theme=dark] .mic{background:#1B2028;box-shadow:inset 0 0 0 1px #2A3140}

/* 我来讲 */
#btnListen.active{background:#4E9C6B;box-shadow:none;color:#fff}
#btnListen.active svg{stroke:#fff}
.composer.listening{background:linear-gradient(180deg,transparent,rgba(78,156,107,.08))}
.composer.listening textarea{box-shadow:inset 0 0 0 1.5px #4E9C6B}
.bar button{white-space:nowrap}

/* 标注按钮挪到黑板角上 */
.pen-btn{position:absolute;right:12px;bottom:56px;width:34px;height:34px;min-height:34px;padding:0;border-radius:50%;background:rgba(255,255,255,.9);box-shadow:0 4px 14px rgba(0,0,0,.35);display:grid;place-items:center;z-index:5}
.pen-btn[hidden]{display:none!important}
.pen-btn svg{width:16px;height:16px;fill:none;stroke:#17181C;stroke-width:1.8;stroke-linecap:round;stroke-linejoin:round}
#btnPen.active{background:#E8C46A}
/* 我来讲按钮（输入框旁） */
.mic.listen svg{stroke:#4E9C6B}
.mic.listen.on{background:#4E9C6B;box-shadow:0 0 0 4px rgba(78,156,107,.18)}
.mic.listen.on svg{stroke:#fff}
.bar .pill{max-width:40%}

/* 回看提示条 */
.back-live{position:absolute;left:12px;right:12px;bottom:12px;display:flex;align-items:center;justify-content:center;gap:10px;min-height:38px;padding:0 14px;border-radius:19px;background:rgba(20,22,28,.98);color:#E8EAEE;font-size:12.5px;box-shadow:0 8px 22px rgba(0,0,0,.4);z-index:6}
.back-live[hidden]{display:none!important}
.back-live b{font-weight:500;color:#8AB6FF}
.back-live span{color:#9AA1AC}

/* 浮层要贴可视区，不能跟着黑板内容滚 */
.stage{position:relative}



/* 回看条别和笔按钮打架 */
.back-live{bottom:10px;left:60px;right:60px}
.pen-btn{bottom:64px}
#btnPen{bottom:64px}
#btnVariant{bottom:110px}


/* 此页静音提示 */
.mute-badge{position:absolute;left:12px;right:12px;bottom:52px;display:flex;align-items:center;justify-content:center;gap:10px;min-height:34px;padding:0 14px;border-radius:17px;background:rgba(20,22,28,.98);color:#E8EAEE;font-size:12px;box-shadow:0 6px 18px rgba(0,0,0,.4);z-index:6}
.mute-badge[hidden]{display:none!important}
.mute-badge b{color:#E8C46A;font-weight:500}
.mute-badge span{color:#9AA1AC}

/* 浮层统一错开：回看条最下，静音条其上，按钮再上 */
.back-live{bottom:8px}
.mute-badge{bottom:48px}
.pen-btn{bottom:96px}
#btnPen{bottom:96px}
#btnClearPen{bottom:96px}
#btnVariant{bottom:142px}
.to-top{bottom:188px}


/* ========== 皮肤 ========== */
html[data-skin=warm]{--bg:#F6F1E7;--card:#FFFDF8;--soft:#EDE4D6;--line:#E8DFD0;--text:#2A231B;--muted:#7A6E5E;--ink:#241E17}
html[data-skin=green]{--bg:#EEF2EE;--card:#FBFDFB;--soft:#DDE6DF;--line:#E1E8E2;--text:#1B2420;--muted:#5F6E66;--ink:#14251D}
html[data-skin=blue]{--bg:#EDF1F7;--card:#FAFCFE;--soft:#DDE6F2;--line:#E0E8F2;--text:#17202B;--muted:#5F6B7A;--ink:#101B2B}

/* 讲完之后的下一步 */
.done-bar{position:absolute;left:12px;right:12px;bottom:18px;display:flex;align-items:center;gap:8px;padding:8px 10px;border-radius:16px;background:#1F2027;border:1px solid rgba(255,255,255,.08);box-shadow:0 10px 26px rgba(0,0,0,.55);z-index:7}
.done-bar[hidden]{display:none!important}
.db-lab{font-size:12px;color:#9AA1AC;flex:1;padding-left:4px}
.db-btn{min-height:32px;padding:0 12px;font-size:12.5px;border-radius:16px;background:rgba(255,255,255,.1);color:#E8EAEE;border:0}
.db-btn.primary{background:#E8EAEE;color:#17181C;font-weight:500}
.db-btn:active{transform:scale(.97)}


.done-bar .db-btn.primary{background:#F2F4F8!important;color:#17181C!important;font-weight:600;box-shadow:0 2px 8px rgba(0,0,0,.3)}
.done-bar .db-btn:not(.primary){background:transparent;border:1px solid rgba(255,255,255,.28);color:#D8DCE4}

/* 手机上长公式会把整页撑宽，右边被裁 */
html,body{max-width:100%;overflow-x:hidden}
.stage,.board,.lines,.prob,.bar,.composer,.tabs{min-width:0}
.prob,.lines,.ln{overflow-wrap:anywhere;word-break:break-word}
.prob .katex,.lines .katex{white-space:normal}
.katex-display{overflow-x:auto;overflow-y:hidden;max-width:100%}

/* ===== 手机端适配（iPhone 刘海屏 / 底部横条） ===== */
/* 底部横条会盖住导航，把安全区垫出来；没刘海时 env() 是 0，不影响桌面 */
.tabs{padding-bottom:calc(6px + env(safe-area-inset-bottom, 0px));margin-bottom:calc(6px + env(safe-area-inset-bottom, 0px))}
.top{padding-top:calc(11px + env(safe-area-inset-top, 0px))}
/* 老浏览器不认 dvh 时退回 vh */
@supports not (height: 100dvh){
  body{height:100vh}
  .board{max-height:calc(100vh - 210px)}
}

/* 手机端触摸手感：iOS 上的惯性滚动 + 别让长按弹菜单 */
.board,.page,.sheet .panel{-webkit-overflow-scrolling:touch}
.board,.lines,.page{-webkit-touch-callout:none}
/* 主要按钮拇指友好：iOS 建议最小 44pt，这里给底部操作和主按钮补到 42-44 */
.db-btn{min-height:38px}
.be-btn{min-height:44px}
#sendBtn{min-height:44px}
#btnListen,#btnMic{min-width:44px;min-height:44px}

/* 深色模式下的浮层按钮：默认那套白底在深色黑板旁边会糊成一片，看不见 */
html[data-theme=dark] .pen-btn{background:rgba(48,53,63,.96);box-shadow:0 4px 14px rgba(0,0,0,.55),inset 0 0 0 1px rgba(255,255,255,.14)}
html[data-theme=dark] .pen-btn svg{stroke:#E8EAEE}
html[data-theme=dark] .to-top{background:rgba(48,53,63,.96);box-shadow:0 4px 14px rgba(0,0,0,.55),inset 0 0 0 1px rgba(255,255,255,.14)}
html[data-theme=dark] .to-top svg{stroke:#E8EAEE}
html[data-theme=dark] .back-live,html[data-theme=dark] .done-bar{background:#2A2F39;border-color:rgba(255,255,255,.16);box-shadow:0 10px 26px rgba(0,0,0,.7)}

/* ===== 字幕层：当前这一句话，单独一条，不跟板书混 ===== */
#caption{
  position:absolute;left:10px;right:10px;bottom:76px;z-index:6;
  font-size:17px;line-height:1.65;color:#F4F6FA;
  text-align:center;padding:11px 16px;border-radius:14px;
  background:rgba(16,18,24,.94);
  box-shadow:0 10px 28px rgba(0,0,0,.55), inset 0 0 0 1px rgba(255,255,255,.08);
  opacity:0;transform:translateY(6px);
  transition:opacity .18s ease, transform .18s ease;
  pointer-events:none;max-height:5.2em;overflow:hidden
}
#caption.on{opacity:1;transform:none}
@media (max-width:430px){
  #caption{font-size:15.5px;padding:9px 13px;bottom:58px;left:8px;right:8px}
}

/* 字幕不压板书：黑板底部留一条空，滚到底时最后几行也能看见 */
.board .lines{padding-bottom:96px}
/* 回看的时候字幕收起来，两个浮层不打架 */
.board.reviewing ~ #caption,#caption.reviewing{opacity:0!important}