:root{
  --topic-ink:#182235;
  --topic-muted:#647085;
  --topic-line:#dfe5ef;
  --topic-blue:#2a5bd7;
  --topic-green:#19735a;
  --topic-amber:#946200;
  --topic-rose:#9b3852;
  --topic-bg:#f7f9fd;
}

body{
  background:linear-gradient(180deg,#f8faff 0%,#f4f6fb 100%);
  color:var(--topic-ink);
}

a{
  color:inherit;
  text-decoration:none;
}

.topic-shell{
  width:min(1120px,calc(100% - 32px));
  margin:0 auto;
  padding:18px 0 44px;
}

.topic-topbar{
  display:flex;
  align-items:center;
  justify-content:space-between;
  gap:16px;
  margin-bottom:18px;
}

.topic-nav,
.topic-actions{
  display:flex;
  align-items:center;
  gap:8px;
  flex-wrap:wrap;
}

.back-link,
.topic-action{
  display:inline-flex;
  align-items:center;
  justify-content:center;
  min-height:38px;
  padding:0 12px;
  border:1px solid var(--topic-line);
  border-radius:8px;
  background:rgba(255,255,255,.92);
  color:var(--topic-muted);
  font-size:14px;
  font-weight:800;
  box-shadow:0 6px 16px rgba(24,34,53,.05);
}

.topic-action.primary{
  border-color:rgba(42,91,215,.35);
  background:#eef3ff;
  color:var(--topic-blue);
}

.figure-model{
  color:var(--topic-muted);
  font-family:ui-monospace,SFMono-Regular,Menlo,Monaco,Consolas,"Liberation Mono",monospace;
  font-size:12px;
}

.topic-hero{
  display:grid;
  grid-template-columns:minmax(0,1.05fr) minmax(320px,.95fr);
  gap:16px;
  align-items:stretch;
  margin-bottom:20px;
}

.topic-intro,
.diagram-panel,
.content-panel{
  border:1px solid var(--topic-line);
  border-radius:8px;
  background:#fff;
  box-shadow:0 10px 26px rgba(24,34,53,.06);
}

.topic-intro{
  display:flex;
  flex-direction:column;
  justify-content:center;
  min-width:0;
  padding:24px;
}

.topic-intro h1{
  margin:0;
  font-size:clamp(28px,3.8vw,42px);
  line-height:1.18;
  letter-spacing:0;
}

.topic-definition{
  max-width:34em;
  margin:18px 0 0;
  color:var(--topic-muted);
  font-size:clamp(16px,1.8vw,18px);
  font-weight:600;
  line-height:1.95;
}

.topic-formula{
  box-sizing:border-box;
  width:100%;
  min-width:0;
  max-width:42em;
  margin-top:20px;
  padding:18px 18px 16px;
  border:1px solid #dce6f7;
  border-radius:8px;
  background:linear-gradient(180deg,#fbfdff 0%,#f6f9ff 100%);
  color:var(--topic-blue);
}

.topic-formula-main,
.topic-formula-sub{
  overflow:visible;
  text-align:center;
}

.topic-formula-main{
  font-size:clamp(20px,2.7vw,31px);
}

.topic-formula-sub{
  margin-top:8px;
  color:var(--topic-muted);
  font-size:clamp(18px,2.1vw,24px);
}

.topic-formula .katex-display{
  margin:0;
}

.topic-formula .katex{
  font-family:KaTeX_Main,"Times New Roman","Hiragino Mincho ProN","Yu Mincho",serif;
  line-height:1.25;
}

.diagram-panel{
  min-height:360px;
  padding:14px;
  display:flex;
  align-items:center;
  justify-content:center;
}

.diagram-panel svg{
  width:100%;
  max-width:520px;
  height:auto;
  display:block;
}

.solid-figure-stage{
  aspect-ratio:1/1;
}

.drawing-preview-image{
  display:block;
  width:100%;
  max-width:520px;
  height:auto;
  border-radius:8px;
}

.drawing-preview{
  background:#fbfcff;
}

.diagram-line{
  stroke:#243047;
  stroke-width:4;
  fill:none;
  stroke-linecap:round;
  stroke-linejoin:round;
}

.diagram-muted{
  stroke:#8d99aa;
  stroke-width:3;
  fill:none;
  stroke-dasharray:9 8;
  stroke-linecap:round;
}

.diagram-fill{
  fill:#eef3ff;
}

.diagram-accent{
  stroke:var(--topic-blue);
  stroke-width:4;
  fill:none;
  stroke-linecap:round;
}

.diagram-point{
  fill:#243047;
}

.diagram-label{
  fill:#243047;
  font-size:22px;
  font-weight:800;
  font-family:system-ui,-apple-system,BlinkMacSystemFont,"Segoe UI",sans-serif;
}

.diagram-note{
  fill:var(--topic-blue);
  font-size:18px;
  font-weight:800;
  font-family:system-ui,-apple-system,BlinkMacSystemFont,"Segoe UI",sans-serif;
}

.content-grid{
  display:grid;
  grid-template-columns:repeat(2,minmax(0,1fr));
  gap:16px;
}

.content-panel{
  padding:18px;
}

.content-panel h2{
  margin:0 0 12px;
  font-size:22px;
  line-height:1.25;
}

.content-panel p,
.content-panel li{
  color:var(--topic-muted);
  font-size:15px;
  line-height:1.75;
}

.content-panel p{
  margin:0;
}

.content-panel ul{
  margin:0;
  padding-left:20px;
}

.definition-only{
  grid-template-columns:1fr;
}

.definition-card{
  border-left:5px solid var(--topic-blue);
}

.formula{
  display:flex;
  align-items:center;
  justify-content:center;
  min-height:70px;
  margin-top:12px;
  border:1px solid #dce6f7;
  border-radius:8px;
  background:#fbfdff;
  color:var(--topic-blue);
  font-size:24px;
  font-weight:900;
}

.model-json{
  display:none;
}

@media (max-width: 860px){
  .topic-hero,
  .content-grid{
    grid-template-columns:1fr;
  }

  .diagram-panel{
    min-height:300px;
  }
}

@media (max-width: 560px){
  .topic-shell{
    width:min(100%,calc(100% - 24px));
    padding-top:14px;
  }

  .topic-topbar{
    display:grid;
    grid-template-columns:repeat(3,minmax(0,1fr));
    gap:8px;
  }

  .topic-nav,
  .topic-actions{
    display:contents;
  }

  .back-link,
  .topic-action{
    min-width:0;
    padding:0 8px;
  }

  .topic-intro{
    padding:18px;
    min-height:190px;
  }

  .topic-formula{
    padding:16px 12px 14px;
  }

  .diagram-panel{
    padding:10px;
  }
}