:root{
  --bg:#f4f7fb;--surface:#ffffff;--surface-2:#f8fafc;--text:#172033;--muted:#64748b;
  --primary:#3656d4;--primary-2:#6d5ce8;--accent:#0f9f8c;--border:#dce4f0;
  --danger:#c2414a;--shadow:0 14px 35px rgba(42,58,101,.09);--radius:22px;
}
:root[data-theme="dark"]{
  --bg:#111827;--surface:#182234;--surface-2:#202c40;--text:#edf2f7;--muted:#9fb0c7;
  --primary:#8296ff;--primary-2:#a68df2;--accent:#4fd1c5;--border:#32425a;
  --danger:#ff8a95;--shadow:0 14px 35px rgba(0,0,0,.25);
}
*{box-sizing:border-box}
html{scroll-behavior:smooth}
body{margin:0;background:var(--bg);color:var(--text);font-family:Pretendard,"Noto Sans KR","Malgun Gothic",sans-serif}
button,input{font:inherit}
button{cursor:pointer}
.topbar{position:sticky;top:0;z-index:20;display:flex;justify-content:space-between;align-items:center;gap:20px;padding:18px 24px;background:linear-gradient(135deg,#263f9c,#7657e8);color:#fff;box-shadow:0 8px 20px rgba(38,63,156,.22)}
.brand-wrap{display:flex;align-items:center;gap:12px}.brand-wrap h1{font-size:24px;margin:0}.brand-wrap p{margin:4px 0 0;opacity:.85;font-size:13px}
.top-actions{display:flex;align-items:center;gap:10px}
.icon-btn,.btn{border:0;border-radius:12px;padding:10px 14px}
.icon-btn{background:rgba(255,255,255,.16);color:#fff}
.btn{background:var(--primary);color:#fff;font-weight:700}
.btn.secondary{background:#fff;color:#3148a4}
.btn.ghost{background:var(--surface-2);color:var(--text);border:1px solid var(--border)}
.btn.danger{color:var(--danger)}
.app-shell{display:grid;grid-template-columns:275px minmax(0,1fr);max-width:1480px;margin:auto}
.sidebar{position:sticky;top:84px;height:calc(100vh - 84px);padding:20px 16px;background:var(--surface);border-right:1px solid var(--border);overflow:auto}
.search-box input{width:100%;padding:12px 13px;border-radius:12px;border:1px solid var(--border);background:var(--surface-2);color:var(--text)}
.chapter-nav{margin-top:14px;display:flex;flex-direction:column;gap:5px}.chapter-nav button{border:0;text-align:left;padding:12px;border-radius:12px;background:transparent;color:var(--text)}
.chapter-nav button:hover,.chapter-nav button.active{background:rgba(54,86,212,.12);color:var(--primary);font-weight:800}
.sidebar-footer{margin-top:18px}
.main{padding:24px;min-width:0}.card{background:var(--surface);border:1px solid var(--border);border-radius:var(--radius);padding:24px;box-shadow:var(--shadow);margin-bottom:22px}
.hero{display:grid;grid-template-columns:1.4fr .8fr;gap:22px;align-items:center;background:linear-gradient(135deg,var(--surface),rgba(54,86,212,.08))}
.hero h2{font-size:clamp(28px,4vw,44px);margin:8px 0 12px}.hero p{color:var(--muted);line-height:1.7}
.eyebrow{font-size:12px;font-weight:900;letter-spacing:.12em;color:var(--primary)}
.progress-card{padding:18px;border-radius:18px;background:var(--surface-2);border:1px solid var(--border)}
.progress-label{display:flex;justify-content:space-between;margin-bottom:10px}.progress-track{height:12px;border-radius:999px;background:var(--border);overflow:hidden}.progress-bar{height:100%;width:0;background:linear-gradient(90deg,var(--primary),var(--primary-2));transition:.3s}
.section-head{display:flex;justify-content:space-between;align-items:center;gap:16px;margin-bottom:18px}.section-head h2{margin:4px 0 0}
.mindmap{display:grid;grid-template-columns:repeat(5,minmax(0,1fr));gap:14px}.mind-node{border:1px solid var(--border);border-radius:17px;padding:16px;background:var(--surface-2);text-align:left;transition:.2s;color:var(--text)}
.mind-node:hover{transform:translateY(-4px);border-color:var(--primary)}.mind-node strong{display:block;font-size:17px}.mind-node small{display:block;color:var(--muted);margin-top:7px;line-height:1.45}
.chapter-header{display:flex;justify-content:space-between;align-items:flex-start;gap:20px;border-bottom:1px solid var(--border);padding-bottom:18px;margin-bottom:8px}.chapter-title h2{font-size:32px;margin:5px 0}.chapter-title p{color:var(--muted);margin:0}
.complete-wrap{display:flex;align-items:center;gap:8px;white-space:nowrap}
.topic{border-bottom:1px solid var(--border);padding:18px 0}.topic:last-child{border:0}.topic summary{font-weight:850;font-size:19px;cursor:pointer}.topic-body{padding-top:12px;color:var(--text);line-height:1.8}.topic-body p{margin:8px 0}.topic-body ul{margin:8px 0;padding-left:22px}
.keyword{display:inline-block;padding:4px 9px;border-radius:999px;background:rgba(54,86,212,.12);color:var(--primary);font-weight:800;font-size:13px;margin:3px}
.example{margin-top:10px;padding:13px;border-left:4px solid var(--accent);background:rgba(15,159,140,.08);border-radius:10px}
.exam-tip{margin-top:10px;padding:13px;border-left:4px solid #e9a23b;background:rgba(233,162,59,.1);border-radius:10px}
.compare-grid{display:grid;grid-template-columns:repeat(2,minmax(0,1fr));gap:14px}.compare-card{border:1px solid var(--border);border-radius:16px;padding:16px;background:var(--surface-2)}
.compare-card h3{margin:0 0 12px}.compare-cols{display:grid;grid-template-columns:1fr 1fr;gap:10px}.compare-col{padding:12px;border-radius:12px;background:var(--surface);border:1px solid var(--border)}
.flash-actions{display:flex;gap:8px}.flashcard{width:100%;min-height:240px;border:0;border-radius:20px;padding:28px;background:linear-gradient(135deg,var(--primary),var(--primary-2));color:#fff;text-align:center}
.flashcard .front{font-size:34px;font-weight:900}.flashcard .back{font-size:20px;line-height:1.8}
.search-results{display:grid;gap:10px}.search-item{border:1px solid var(--border);border-radius:13px;padding:14px;background:var(--surface-2)}.search-item button{border:0;background:none;color:var(--primary);font-weight:800;padding:0}
.hidden{display:none!important}.mobile-only{display:none}.exam-mode .topic-body p,.exam-mode .example{display:none}.exam-mode .topic-body ul{margin:6px 0}.exam-mode .topic{padding:10px 0}
footer{padding:28px;text-align:center;color:var(--muted)}
@media(max-width:1050px){.mindmap{grid-template-columns:repeat(3,1fr)}.compare-grid{grid-template-columns:1fr}}
@media(max-width:820px){.mobile-only{display:inline-flex}.app-shell{grid-template-columns:1fr}.sidebar{position:fixed;left:-290px;top:0;z-index:50;width:275px;height:100vh;transition:.25s;box-shadow:var(--shadow)}.sidebar.open{left:0}.main{padding:16px}.hero{grid-template-columns:1fr}.mindmap{grid-template-columns:repeat(2,1fr)}.topbar{padding:14px}.brand-wrap h1{font-size:19px}.brand-wrap p{display:none}}
@media(max-width:520px){.mindmap{grid-template-columns:1fr}.compare-cols{grid-template-columns:1fr}.section-head,.chapter-header{align-items:flex-start;flex-direction:column}.top-actions .secondary{display:none}.card{padding:18px}}