:root{--bg:#ffffff;--text:#0b1220;--muted:#6b7280;--primary:#2477ff;--primary-ink:#fff;--danger:#ff3b30;--card:#f7f8fa;--border:#e5e7eb}
*{box-sizing:border-box}
html,body{margin:0;padding:0;background:var(--bg);color:var(--text);font-family:-apple-system,BlinkMacSystemFont,"Segoe UI",Roboto,Helvetica,Arial,"Apple Color Emoji","Segoe UI Emoji"}
.app-header{padding:24px 16px;text-align:center}
.app-header h1{margin:0;font-size:22px;font-weight:700}
.app-header .subtitle{margin:4px 0 0;color:var(--muted);font-size:14px}
.app-container{max-width:1080px;margin:0 auto;padding:0 16px 64px}
.screen{display:none}
.screen.active{display:block}
.card{background:var(--card);border:1px solid var(--border);border-radius:14px;padding:16px}
.actions{margin-top:16px;display:flex;gap:12px}
.field{margin-top:12px;display:flex;flex-direction:column;gap:6px}
.select{appearance:none;border:1px solid var(--border);background:#fff;border-radius:10px;padding:10px 12px;font-size:14px}
.btn{appearance:none;border:1px solid var(--border);background:#fff;color:var(--text);padding:10px 14px;border-radius:10px;font-size:14px;cursor:pointer}
.btn.primary{background:var(--primary);border-color:var(--primary);color:var(--primary-ink)}
.btn.danger{background:var(--danger);border-color:var(--danger);color:#fff}
.btn:disabled{opacity:.6;cursor:not-allowed}
.exam-topbar{display:flex;justify-content:space-between;align-items:center;gap:8px;padding:8px 0;position:sticky;top:0;background:var(--bg);z-index:5;border-bottom:1px solid var(--border)}
.exam-layout{display:grid;grid-template-columns:220px 1fr;gap:16px;margin-top:12px}
.navigator{background:var(--card);border:1px solid var(--border);border-radius:12px;padding:8px;max-height:70vh;overflow:auto}
.navigator .nav-grid{display:grid;grid-template-columns:repeat(5,1fr);gap:6px}
.nav-section{grid-column:1/-1;color:var(--muted);font-size:12px;padding:4px 2px}
.nav-item{border:1px solid var(--border);border-radius:8px;padding:8px;text-align:center;font-size:12px;background:#fff;cursor:pointer}
.nav-item.answered{background:#e6f0ff;border-color:#cfe0ff}
.nav-item.current{outline:2px solid var(--primary)}
.question-area{display:flex;flex-direction:column;gap:12px}
.question-card{background:var(--card);border:1px solid var(--border);border-radius:12px;padding:16px}
.question-title{margin:0 0 12px;font-weight:600}
.options{display:flex;flex-direction:column;gap:8px}
.exam-actions{display:flex;gap:8px;margin-top:8px}
.app-footer{padding:16px;text-align:center;color:var(--muted);border-top:1px solid var(--border)}
.answer-review{margin-top:16px;display:flex;flex-direction:column;gap:8px}
@media (max-width:900px){.exam-layout{grid-template-columns:1fr}.navigator{order:2}.question-area{order:1}}