:root{
  --bg:#f7f8fb;
  --card:#ffffff;
  --muted:#6b7280;
  --accent-foundations:#eef0f2;
  --accent-basic:#eef6ff;
  --accent-trees:#ecfdf5;
  --accent-graph:#fff7ed;
  --accent-dp:#fff0f6;
  --border:#e6eef8;
  --radius:10px;
  --text:#0f172a;
  font-family: Inter, system-ui, -apple-system, 'Segoe UI', Roboto, Arial;
}
*{box-sizing:border-box}
body{background:var(--bg);margin:20px;-webkit-font-smoothing:antialiased}
.container{max-width:1000px;margin:0 auto}
.app-header{display:flex;justify-content:space-between;align-items:center;margin-bottom:14px}
.app-header h1{margin:0;font-size:18px}
.header-actions{display:flex;gap:12px;align-items:center}
.btn{border:1px solid rgba(15,23,42,0.06);background:white;padding:8px 10px;border-radius:8px;font-size:13px;cursor:pointer}
.muted{color:var(--muted);font-size:13px}
.group-card{background:var(--card);border-radius:var(--radius);border:1px solid var(--border);padding:12px;margin-bottom:16px;box-shadow:0 6px 18px rgba(15,23,42,0.03)}
.group-heading{font-size:12px;color:var(--muted);text-transform:uppercase;letter-spacing:0.8px;margin-bottom:10px}
.topic-list{display:flex;flex-direction:column;gap:8px}
.topic{display:flex;align-items:center;justify-content:space-between;padding:10px;border-radius:8px;transition:transform .12s ease}
.topic:hover{transform:translateY(-2px)}
.topic-left{display:flex;gap:12px;align-items:center}
.topic-number{font-weight:600;width:44px;color:#0b1220}
.topic-title{font-size:14px}
.topic-actions{display:flex;gap:8px;align-items:center}
.btn-small{padding:6px 8px;min-width:36px;font-size:13px}
.btn-complete{background:#ecfdf5;border-color:#bbf7d0;color:#065f46}
.topic-body{display:none;margin-top:8px;padding:12px;border-radius:8px;background:rgba(15,23,42,0.02);font-size:13px;line-height:1.45}
.group-foundations .topic{background:var(--accent-foundations)}
.group-basic .topic{background:var(--accent-basic)}
.group-trees .topic{background:var(--accent-trees)}
.group-graphs .topic{background:var(--accent-graph)}
.group-dp .topic{background:var(--accent-dp)}
.app-footer{margin-top:24px;font-size:13px;color:var(--muted)}