:root{--accent: #2563eb;--accent-dark: #1d4ed8;--accent-soft: #eff6ff;--green: #16a34a;--green-soft: #f0fdf4;--red: #dc2626;--red-soft: #fef2f2;--amber: #d97706;--bg: #f8fafc;--surface: #ffffff;--border: #e5e7eb;--text: #111827;--text-muted: #6b7280;--radius: 10px;--radius-sm: 8px;--shadow: 0 1px 3px rgba(0, 0, 0, .05);--shadow-md: 0 4px 12px rgba(0, 0, 0, .08);--sidebar-w: 240px}*{box-sizing:border-box}html,body,#root{margin:0;height:100%}body{font-family:Inter,-apple-system,BlinkMacSystemFont,Segoe UI,Roboto,sans-serif;background:var(--bg);color:var(--text);font-size:15px;line-height:1.55;-webkit-font-smoothing:antialiased}a{color:var(--accent);text-decoration:none}h1,h2,h3{line-height:1.25;margin:0 0 .5em}button{font-family:inherit;font-size:14px;cursor:pointer}.btn{display:inline-flex;align-items:center;justify-content:center;gap:6px;padding:9px 16px;border:1px solid transparent;border-radius:var(--radius-sm);font-weight:600;background:var(--accent);color:#fff;transition:background 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var(--accent-soft)}label{display:block;font-weight:600;font-size:13px;margin-bottom:6px;color:var(--text)}.field{margin-bottom:16px}.shell{display:flex;min-height:100vh}.sidebar{width:var(--sidebar-w);flex-shrink:0;background:var(--surface);border-right:1px solid var(--border);padding:20px 14px;display:flex;flex-direction:column;gap:4px;position:sticky;top:0;height:100vh}.sidebar .brand{display:flex;align-items:center;gap:8px;font-weight:700;font-size:18px;padding:6px 10px 18px}.nav-link{display:flex;align-items:center;gap:10px;padding:9px 12px;border-radius:var(--radius-sm);color:var(--text-muted);font-weight:500}.nav-link:hover{background:#f3f4f6;color:var(--text)}.nav-link.active{background:var(--accent-soft);color:var(--accent);font-weight:600}.main{flex:1;min-width:0;display:flex;flex-direction:column}.topbar{height:60px;border-bottom:1px solid var(--border);background:var(--surface);display:flex;align-items:center;justify-content:space-between;padding:0 24px;gap:12px}.topbar 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12px;font-size:14px;margin-bottom:14px}.row{display:flex;gap:12px;align-items:center}.grid{display:grid;gap:16px}.grid-3{grid-template-columns:repeat(3,1fr)}.grid-2{grid-template-columns:repeat(2,1fr)}.page-title{font-size:22px;font-weight:700;margin-bottom:4px}.page-sub{color:var(--text-muted);margin-bottom:22px}.tag{display:inline-block;background:var(--accent-soft);color:var(--accent);border-radius:999px;padding:2px 10px;font-size:12px;font-weight:600;margin-right:6px}.spinner{display:inline-block;width:20px;height:20px;border:2px solid var(--border);border-top-color:var(--accent);border-radius:50%;animation:spin .7s linear infinite}@keyframes spin{to{transform:rotate(360deg)}}.center-screen{min-height:100vh;display:flex;align-items:center;justify-content:center}.stat-card{text-align:center}.stat-value{font-size:34px;font-weight:700;color:var(--accent)}.stat-label{color:var(--text-muted);font-size:13px;text-transform:uppercase;letter-spacing:.03em}.bar-row{display:grid;grid-template-columns:140px 1fr 48px;align-items:center;gap:10px;margin-bottom:10px;font-size:13px}.bar-track{background:#f1f5f9;border-radius:999px;height:12px;overflow:hidden}.bar-fill{height:100%;background:var(--accent);border-radius:999px;transition:width .4s ease}.table{width:100%;border-collapse:collapse;font-size:14px}.table th,.table td{text-align:left;padding:10px 12px;border-bottom:1px solid var(--border)}.table th{color:var(--text-muted);font-weight:600;font-size:12px;text-transform:uppercase;letter-spacing:.03em;cursor:pointer;-webkit-user-select:none;user-select:none}.table tbody 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.choice-letter{background:var(--red);color:#fff;border-color:var(--red)}.explanation{margin-top:20px;padding:18px;border-radius:var(--radius);background:#f8fafc;border:1px solid var(--border)}mark{background:#fde68a;padding:0 1px}.tool-btn{background:none;border:1px solid var(--border);border-radius:var(--radius-sm);padding:6px 10px;color:var(--text-muted);display:inline-flex;align-items:center;gap:6px}.tool-btn.active{color:var(--amber);border-color:var(--amber);background:#fffbeb}.nav-strip{display:flex;flex-wrap:wrap;gap:6px;margin-top:16px}.nav-dot{width:34px;height:34px;border-radius:var(--radius-sm);border:1px solid var(--border);background:var(--surface);font-size:13px;font-weight:600;color:var(--text-muted)}.nav-dot.answered{background:var(--accent);color:#fff;border-color:var(--accent)}.nav-dot.flagged{border-color:var(--amber);color:var(--amber)}.nav-dot.current{outline:2px solid 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