:root{
  --ink:#102235;
  --muted:#526477;
  --deep:#07334c;
  --line:#d8e5eb;
  --paper:#ffffff;
  --mist:#eef6f8;
  --soft:#f8fbfd;
  --accent:#0b6fae;
  --gold:#d8a447;
}
*{box-sizing:border-box}
body{margin:0;background:var(--mist);color:var(--ink);font-family:Arial,"Microsoft YaHei",sans-serif}
a{color:inherit}
.site-hero{min-height:430px;background:
  linear-gradient(135deg,rgba(7,51,76,.96),rgba(8,80,112,.82)),
  radial-gradient(circle at 78% 18%,rgba(216,164,71,.35),transparent 28%),
  linear-gradient(90deg,#07334c,#0b6fae);color:#fff}
.topbar{width:min(1180px,calc(100% - 32px));margin:0 auto;display:flex;align-items:center;justify-content:space-between;gap:18px;padding:22px 0}
.brand{display:flex;align-items:center;gap:10px;font-weight:800;letter-spacing:.02em}
.brand-mark{display:grid;place-items:center;width:34px;height:34px;border:1px solid rgba(255,255,255,.35);border-radius:8px;background:rgba(255,255,255,.12)}
.top-links{display:flex;align-items:center;justify-content:flex-end;gap:10px;font-size:14px;flex-wrap:wrap}
.top-links a{min-height:36px;display:inline-flex;align-items:center;text-decoration:none;color:rgba(255,255,255,.84);padding:0 4px}
.top-links a:hover{color:#fff}
.top-links .analysis-cta{min-height:42px;padding:0 18px;border:1px solid rgba(255,255,255,.48);border-radius:999px;background:#d8a447;color:#102235;font-weight:900;box-shadow:0 12px 28px rgba(216,164,71,.34)}
.top-links .analysis-cta:hover{background:#f0c468;color:#102235}
.hero-inner{width:min(1180px,calc(100% - 32px));margin:0 auto;padding:58px 0 66px}
.eyebrow{margin:0 0 12px;color:#b8dce9;font-weight:800;text-transform:uppercase;letter-spacing:.11em}
h1{max-width:760px;margin:0;font-size:clamp(36px,6vw,70px);line-height:1.05;letter-spacing:0}
.hero-copy{max-width:680px;margin:22px 0 0;color:#d7eaf0;font-size:18px;line-height:1.75}
.hero-stats{display:grid;grid-template-columns:repeat(4,minmax(120px,1fr));gap:12px;max-width:760px;margin-top:30px}
.stat{padding:14px 16px;border:1px solid rgba(255,255,255,.22);border-radius:8px;background:rgba(255,255,255,.09)}
.stat strong{display:block;font-size:26px}.stat span{display:block;margin-top:4px;color:#c7dce5;font-size:13px}
main{width:min(1180px,calc(100% - 32px));margin:0 auto 64px}
.toolbar{display:flex;gap:18px;align-items:end;justify-content:space-between;padding:32px 0 16px}
h2{margin:0 0 8px;color:var(--deep);font-size:28px;line-height:1.2}.toolbar p{margin:0;color:var(--muted);line-height:1.65}
.search-box{display:flex;align-items:center;gap:10px;width:min(420px,100%);padding:10px 12px;border:1px solid var(--line);border-radius:8px;background:#fff;color:var(--muted)}
.search-box input{width:100%;border:0;outline:0;color:var(--ink);font:inherit;background:transparent}
.chapter-tabs{display:flex;gap:10px;overflow:auto;padding:4px 0 18px}
.tab{flex:0 0 auto;border:1px solid var(--line);border-radius:8px;background:#fff;color:var(--deep);padding:10px 13px;font-weight:800;cursor:pointer}
.tab.active{border-color:var(--deep);background:var(--deep);color:#fff}
.layout{display:grid;grid-template-columns:360px minmax(0,1fr);gap:18px;align-items:start}
.lesson-list{display:grid;gap:10px;max-height:calc(100vh - 24px);overflow:auto;position:sticky;top:12px;padding-right:4px}
.lesson-card{border:1px solid var(--line);border-radius:8px;background:#fff;padding:14px;box-shadow:0 10px 26px rgba(9,34,53,.05);cursor:pointer}
.lesson-card.active{border-color:var(--accent);box-shadow:0 12px 30px rgba(11,111,174,.16)}
.lesson-card h3{margin:0;color:var(--deep);font-size:16px;line-height:1.35}
.meta{display:flex;gap:8px;flex-wrap:wrap;margin-top:10px;color:var(--muted);font-size:12px}
.pill{padding:4px 7px;border-radius:999px;background:#edf5f8;color:#25546b}
.lesson-panel{min-height:480px;border:1px solid var(--line);border-radius:10px;background:#fff;box-shadow:0 14px 36px rgba(9,34,53,.06);overflow:hidden}
.lesson-head{padding:26px 28px;border-bottom:1px solid var(--line);background:linear-gradient(180deg,#fff,#f7fbfd)}
.lesson-head h2{font-size:30px}.lesson-head p{color:var(--muted);line-height:1.75;margin:10px 0 0}
.key-grid{display:grid;grid-template-columns:repeat(auto-fit,minmax(210px,1fr));gap:10px;margin-top:18px}
.key{padding:12px;border-left:3px solid var(--gold);background:#fff8ea;border-radius:6px;line-height:1.55}
.lesson-panel a{color:var(--accent);font-weight:800;text-decoration:none;border-bottom:1px solid rgba(11,111,174,.28);overflow-wrap:anywhere}
.lesson-panel a:hover{border-bottom-color:var(--accent)}
.video-block{margin-top:22px;border:1px solid #c9dce5;border-radius:8px;background:#eef6f8;overflow:hidden}
.video-frame{position:relative;aspect-ratio:16/9;background:#0b1720}
.video-frame iframe{position:absolute;inset:0;width:100%;height:100%;border:0}
.video-meta{display:flex;gap:12px;align-items:center;justify-content:space-between;padding:12px 14px;color:var(--muted);font-size:14px}
.video-meta strong{color:var(--deep)}
.video-meta a{white-space:nowrap}
.concept-block{margin-top:22px;border:1px solid #c9dce5;border-radius:8px;background:#fff;overflow:hidden}
.concept-title{display:flex;align-items:center;gap:10px;padding:14px 16px;border-bottom:1px solid var(--line);background:#edf6f8}
.concept-title span{display:grid;place-items:center;width:28px;height:28px;border-radius:8px;background:var(--deep);color:#fff;font-weight:800}
.concept-title h3{margin:0;color:var(--deep);font-size:18px;line-height:1.35}
.concept-body{display:grid;grid-template-columns:minmax(0,1.1fr) minmax(260px,.9fr);gap:16px;padding:16px}
.concept-body p{margin:0;color:var(--muted);line-height:1.75}
.concept-steps{margin:0;padding-left:18px;color:var(--muted);line-height:1.7}
.concept-note{grid-column:1/-1;padding:12px 14px;border-left:3px solid var(--gold);border-radius:6px;background:#fff8ea;color:#5b4b24;line-height:1.65}
.slide-section{padding:24px 28px}
.slide{padding:24px 0;border-top:1px solid var(--line)}
.slide:first-child{border-top:0}
.slide h3{margin:0 0 10px;color:var(--deep);font-size:18px;line-height:1.35}
.slide ul{margin:0;padding-left:18px;color:var(--muted);line-height:1.7}
.thumbs{display:grid;grid-template-columns:1fr;gap:18px;margin-top:18px}
.thumbs a{display:block;min-width:0}
.thumbs img{display:block;width:100%;height:auto;object-fit:contain;background:var(--soft);border:1px solid #d8e5eb;border-radius:8px;padding:12px;box-shadow:0 10px 24px rgba(9,34,53,.05)}
.empty{padding:34px;color:var(--muted)}
@media (max-width:900px){
  .topbar{align-items:flex-start;flex-direction:column}.top-links{width:100%;justify-content:flex-start}.top-links .analysis-cta{width:100%;justify-content:center}
  .toolbar{display:grid}.hero-stats{grid-template-columns:repeat(2,1fr)}.layout{grid-template-columns:1fr}.lesson-list{position:static;max-height:none}.thumbs{grid-template-columns:1fr}.video-meta{display:grid}
  .concept-body{grid-template-columns:1fr}
}