/* AI 学习视频栏目 */
:root{--lv-rule:#e3ded2;--lv-ink:#1a1a1a;--lv-muted:#6b6560;--lv-blue:#2f5fd0;--lv-paper:#fbf8f1}
[data-theme="dark"]{--lv-rule:#2c2c38;--lv-ink:#e8e6e3;--lv-muted:#9a948e;--lv-blue:#7ea2ff;--lv-paper:#14141b}
.prototype-learn main{max-width:1380px;margin:0 auto;padding:1.5rem 1.25rem 3rem;color:var(--lv-ink)}
.lv-head{padding:1.5rem 0 1.75rem;border-bottom:2px solid var(--lv-ink)}
.lv-head h1{margin:.3rem 0 .7rem;font-size:clamp(1.7rem,3.4vw,2.6rem)}
.lv-dek{margin:0 0 .6rem;max-width:70ch;line-height:1.8}
.lv-note{margin:0;max-width:78ch;font-size:.84rem;line-height:1.7;color:var(--lv-muted)}

.lv-group{padding:2rem 0 .5rem;border-bottom:1px solid var(--lv-rule)}
.lv-group>header{margin-bottom:1.2rem}
.lv-group h2{margin:0 0 .3rem;font-size:1.3rem}
.lv-group>header p{margin:0;font-size:.88rem;color:var(--lv-muted)}
.lv-grid{display:grid;gap:1.5rem;grid-template-columns:repeat(auto-fill,minmax(300px,1fr))}

.lv-card{display:flex;flex-direction:column;border:1px solid var(--lv-rule);border-radius:10px;overflow:hidden;background:var(--lv-paper)}
/* 16:9 的播放位。视频与 iframe 都撑满, 免得卡片高度参差不齐。 */
.lv-media{position:relative;aspect-ratio:16/9;background:#000}
.lv-media video,.lv-media iframe,.lv-media img{position:absolute;inset:0;width:100%;height:100%;border:0;object-fit:cover;display:block}
.lv-cover{display:block;position:absolute;inset:0}
.lv-cover::after{content:"↗";position:absolute;right:.6rem;bottom:.5rem;color:#fff;font-size:1.1rem;
  text-shadow:0 1px 4px rgba(0,0,0,.6)}
.lv-info{padding:.9rem 1rem 1.1rem;display:flex;flex-direction:column;gap:.4rem}
.lv-info h3{margin:0;font-size:1rem;line-height:1.5}
.lv-meta{margin:0;font-size:.8rem;color:var(--lv-muted)}
.lv-sum{margin:.2rem 0 0;font-size:.85rem;line-height:1.65;color:var(--lv-muted)}
.lv-credit{margin:.3rem 0 0;font-size:.76rem;color:var(--lv-muted)}
.lv-credit a{color:var(--lv-blue)}

.lv-badge{align-self:flex-start;font-size:.72rem;padding:.15rem .5rem;border-radius:3px;letter-spacing:.04em}
.lv-badge--self{background:rgba(47,95,208,.12);color:var(--lv-blue)}
.lv-badge--bili{background:rgba(251,114,153,.16);color:#c2185b}
.lv-badge--link{background:rgba(120,120,120,.14);color:var(--lv-muted)}
[data-theme="dark"] .lv-badge--bili{color:#ff9ab8}
@media(max-width:520px){.lv-grid{grid-template-columns:1fr}}

/* 跳转链接应当只在键盘聚焦时出现, 否则会明晃晃地印在页首。 */
.prototype-learn .prototype-skip{position:absolute;left:-9999px;top:0}
.prototype-learn .prototype-skip:focus{left:.5rem;top:.5rem;z-index:99;padding:.4rem .8rem;
  background:var(--lv-paper);border:1px solid var(--lv-ink);border-radius:4px}

/* 知识分支目录 */
.lv-toc{display:flex;flex-wrap:wrap;gap:.5rem;margin-top:1.1rem}
.lv-toc a{display:inline-flex;align-items:baseline;gap:.35rem;padding:.3rem .7rem;
  border:1px solid var(--lv-rule);border-radius:999px;font-size:.85rem;
  color:var(--lv-ink);text-decoration:none;background:var(--lv-paper)}
.lv-toc a:hover{border-color:var(--lv-blue);color:var(--lv-blue)}
.lv-toc b{font-weight:600;font-size:.76rem;color:var(--lv-muted)}
.lv-group{scroll-margin-top:5rem}
.lv-library-layout{display:grid;grid-template-columns:minmax(210px,250px) minmax(0,1fr);gap:2rem;align-items:start}
.lv-library-content{min-width:0}
.lv-tree{position:sticky;top:5.25rem;max-height:calc(100dvh - 6.5rem);overflow:auto;margin-top:2rem;
  padding:.35rem 1rem .8rem 0;border-right:1px solid var(--lv-rule);scrollbar-width:thin}
.lv-tree__branch{border-bottom:1px solid var(--lv-rule)}
.lv-tree__branch summary{list-style:none;cursor:pointer}
.lv-tree__branch summary::-webkit-details-marker{display:none}
.lv-tree__branch summary{display:grid;grid-template-columns:1rem minmax(0,1fr) auto;align-items:center;
  gap:.5rem;padding:.72rem .15rem;color:var(--lv-ink);font-size:.9rem;line-height:1.4}
.lv-tree__branch summary::before{content:"+";width:1rem;color:var(--lv-muted)}
.lv-tree__branch[open] summary::before{content:"−"}
.lv-tree__branch summary b{font-size:.72rem;color:var(--lv-muted);font-variant-numeric:tabular-nums}
.lv-tree__branch[data-current="true"] summary{color:var(--lv-blue);font-weight:650}
.lv-tree__branch ul{list-style:none;margin:0 0 .65rem;padding:0 0 0 1.2rem;display:grid;gap:.12rem}
.lv-tree__branch li a{display:block;padding:.28rem .35rem;color:var(--lv-muted);text-decoration:none;
  font-size:.78rem;line-height:1.4;border-left:2px solid transparent;white-space:nowrap;overflow:hidden;text-overflow:ellipsis}
.lv-tree__branch li a[aria-current]{color:var(--lv-blue);border-left-color:var(--lv-blue);font-weight:650}
.lv-tree__video{list-style:disc}
.lv-tree__video::marker{color:var(--lv-muted);font-size:.75em}
.lv-tree__video:has(a[aria-current])::marker{color:var(--lv-blue)}
.lv-tree__all a{font-weight:650;color:var(--lv-ink)}
.lv-tree__branch li a:hover,.lv-tree__branch li a:focus-visible{color:var(--lv-blue);border-left-color:var(--lv-blue)}
.lv-tree-mobile{display:none}
.lv-card{scroll-margin-top:5rem}
@media(max-width:900px){
  .lv-library-layout{display:block}.lv-tree--desktop{display:none}.lv-tree-mobile{display:block;margin-top:1.1rem}
  .lv-tree-mobile>details{border:1px solid var(--lv-rule);border-radius:10px;background:var(--lv-paper)}
  .lv-tree-mobile>details>summary{padding:.75rem 1rem;cursor:pointer;font-weight:650}
  .lv-tree-mobile nav{padding:0 1rem .7rem}.lv-tree-mobile .lv-tree__branch ul{max-height:12rem;overflow:auto}
}
.lv-badge--pick{background:rgba(16,138,88,.14);color:#0b7a4d}
[data-theme="dark"] .lv-badge--pick{color:#5fd6a2}

/* 封面 + 播放按钮。不直接嵌 iframe: 一页 46 个跨域播放器拖慢加载, 而且 B 站在小尺寸
   未交互状态下会收起控制栏, 用户看到的就是"没有全屏按钮"。 */
.lv-play{position:absolute;inset:0;width:100%;height:100%;padding:0;border:0;
  background:#000;cursor:pointer;display:block}
.lv-play img{position:absolute;inset:0;width:100%;height:100%;object-fit:cover}
.lv-play__icon{position:absolute;left:50%;top:50%;transform:translate(-50%,-50%);
  width:54px;height:54px;line-height:52px;border-radius:50%;font-size:1.1rem;
  background:rgba(0,0,0,.55);color:#fff;border:2px solid rgba(255,255,255,.85)}
.lv-play:hover .lv-play__icon{background:rgba(47,95,208,.85)}

/* 大屏浮层: 播放器足够大, 控件与全屏键必然出现 */
.lv-modal{position:fixed;inset:0;z-index:2147483000;background:rgba(0,0,0,.82);
  display:flex;align-items:center;justify-content:center;padding:1rem}
.lv-modal[hidden]{display:none}
.lv-modal__box{width:min(1100px,94vw);display:flex;flex-direction:column;gap:.5rem}
.lv-modal__bar{display:flex;align-items:center;justify-content:space-between;gap:1rem;color:#fff}
.lv-modal__title{font-size:.95rem;line-height:1.5;overflow:hidden;
  display:-webkit-box;-webkit-line-clamp:2;-webkit-box-orient:vertical}
.lv-modal__close{background:none;border:0;color:#fff;font-size:1.3rem;cursor:pointer;padding:.2rem .5rem}
.lv-modal__frame{position:relative;aspect-ratio:16/9;background:#000;border-radius:8px;overflow:hidden}
.lv-modal__frame iframe{position:absolute;inset:0;width:100%;height:100%;border:0}



/* 浮层自己的控制条。播放器那套控件是 B 站的代码, 点了没反应我们改不动, 所以关键动作
   （全屏、去 B 站）都用自己的按钮。 */
.lv-modal__tools{display:flex;align-items:center;gap:.75rem;flex-shrink:0}
.lv-modal__full,.lv-modal__out{background:rgba(255,255,255,.14);border:0;color:#fff;
  font-size:.82rem;padding:.34rem .7rem;border-radius:5px;cursor:pointer;text-decoration:none;
  white-space:nowrap}
.lv-modal__full:hover,.lv-modal__out:hover{background:rgba(255,255,255,.26)}
/* 前两级原生全屏都被环境拒绝时的退路: 铺满视口。保留顶部工具条, 画面按 16:9 居中,
   免得被拉成一条黑带。 */
.lv-modal--max{padding:0}
.lv-modal--max .lv-modal__box{width:100vw;height:100dvh;max-width:none;gap:0}
.lv-modal--max .lv-modal__bar{padding:.5rem .75rem;background:#000}
.lv-modal--max .lv-modal__frame{aspect-ratio:auto;flex:1;border-radius:0;
  display:flex;align-items:center;justify-content:center}
.lv-modal--max .lv-modal__frame iframe{position:static;width:100%;height:100%}