:root{--bg: #f6f8fb;--card: #ffffff;--text: #1a2332;--muted: #5c6b7f;--primary: #3b6ff5;--primary-soft: #e8efff;--border: #e2e8f0;--success: #16a34a;--danger: #dc2626;--radius: 14px;--shadow: 0 8px 30px rgba(26, 35, 50, .06);--topbar-h: 52px}*{box-sizing:border-box}body{margin:0;font-family:Inter,system-ui,-apple-system,Segoe UI,Roboto,sans-serif;background:var(--bg);color:var(--text);line-height:1.5}a{color:var(--primary);text-decoration:none}.container{width:min(1100px,92vw);margin:0 auto;padding:24px 0 48px}.card{background:var(--card);border:1px solid var(--border);border-radius:var(--radius);box-shadow:var(--shadow);padding:20px}.grid{display:grid;gap:16px}.grid-2{grid-template-columns:repeat(auto-fit,minmax(260px,1fr))}.topbar{background:var(--card);border-bottom:1px solid var(--border);padding:14px 0;position:sticky;top:0;z-index:10}.topbar-inner{width:min(1100px,92vw);margin:0 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auto;font-size:.75rem;color:var(--muted, #64748b)}.lesson-group-title{flex:1 1 auto;font-weight:600;min-width:0}.lesson-group-badge{flex:0 0 auto;padding:2px 8px;border-radius:999px;background:var(--primary-soft);color:var(--primary);font-size:.75rem;font-weight:600}.lesson-group-meta{flex:1 1 100%;display:flex;gap:12px;font-size:.8rem;color:var(--muted, #64748b);padding-left:1.25rem}.lesson-group-body{display:flex;flex-direction:column;gap:12px;padding:12px 14px;border-top:1px solid var(--border);max-height:min(52vh,520px);overflow-y:auto;overflow-x:hidden;overscroll-behavior:contain;-webkit-overflow-scrolling:touch}.lesson-group.collapsed .lesson-group-body{display:none}.msg{max-width:85%;padding:12px 14px;border-radius:12px;white-space:pre-wrap}.msg.user{align-self:flex-end;background:var(--primary);color:#fff}.msg.assistant{align-self:flex-start;background:#f1f5f9;border:1px solid var(--border)}.msg.thinking{align-self:flex-start;background:#fff7ed;border:1px dashed 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.topbar--chat{display:none}.container--chat{width:100%;max-width:100%;margin:0;padding:0;height:100dvh;height:100svh;overflow:hidden;display:flex;flex-direction:column}.chat-page-shell{flex:1;display:flex;flex-direction:column;gap:0;min-height:0;height:100%;overflow:hidden}.chat-sidebar{display:none}.chat-main{flex:1;display:flex;flex-direction:column;min-height:0;height:100%;border:none;border-radius:0;box-shadow:none;padding:0;background:var(--bg);position:relative;overflow:hidden}.chat-mobile-header{display:flex;align-items:center;gap:10px;padding:max(10px,env(safe-area-inset-top,0px)) 12px 10px;background:var(--card);border-bottom:1px solid var(--border);flex-shrink:0}.chat-back{flex:0 0 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