*,*:before,*:after{box-sizing:border-box;margin:0;padding:0}:root{--primary: #1a56db;--primary-dark: #1e429f;--success: #057a55;--danger: #c81e1e;--warning: #9f580a;--bg: #f9fafb;--card: #ffffff;--border: #e5e7eb;--text: #111827;--muted: #6b7280;--radius: 12px}body{font-family:-apple-system,BlinkMacSystemFont,Segoe UI,sans-serif;background:var(--bg);color:var(--text);line-height:1.6;-webkit-tap-highlight-color:transparent}.container{max-width:480px;margin:0 auto;padding:0 16px}.bottom-nav{position:fixed;bottom:0;left:0;right:0;background:var(--card);border-top:1px solid var(--border);display:flex;z-index:100;padding-bottom:env(safe-area-inset-bottom)}.nav-item{flex:1;display:flex;flex-direction:column;align-items:center;padding:8px 4px;font-size:11px;color:var(--muted);text-decoration:none;border:none;background:none;cursor:pointer}.nav-item.active{color:var(--primary)}.nav-icon{font-size:22px;margin-bottom:2px}.card{background:var(--card);border:1px solid var(--border);border-radius:var(--radius);padding:16px;margin-bottom:12px}.btn{display:inline-flex;align-items:center;justify-content:center;padding:12px 20px;border-radius:8px;font-size:15px;font-weight:600;cursor:pointer;border:none;text-decoration:none;transition:opacity .15s}.btn:active{opacity:.8}.btn-primary{background:var(--primary);color:#fff;width:100%}.btn-outline{background:transparent;border:2px solid var(--primary);color:var(--primary)}.option-btn{width:100%;text-align:left;padding:9px 14px;margin-bottom:5px;border-radius:10px;border:2px solid var(--border);background:var(--card);font-size:18.5px;font-weight:600;cursor:pointer;transition:all .15s}.option-btn:hover{border-color:var(--primary)}.option-btn.correct{border-color:var(--success);background:#f0fdf4;color:var(--success)}.option-btn.wrong{border-color:var(--danger);background:#fff5f5;color:var(--danger)}.option-btn.selected{border-color:var(--primary);background:#eff6ff}.progress-bar{height:6px;background:var(--border);border-radius:3px;overflow:hidden}.progress-fill{height:100%;background:var(--primary);border-radius:3px;transition:width .3s}.badge{display:inline-block;padding:2px 8px;border-radius:99px;font-size:12px;font-weight:600}.badge-success{background:#dcfce7;color:var(--success)}.badge-danger{background:#fee2e2;color:var(--danger)}.badge-primary{background:#dbeafe;color:var(--primary)}.mastery-bar{display:flex;align-items:center;gap:8px;margin-bottom:10px}.mastery-label{font-size:13px;flex:1}.mastery-track{flex:2;height:8px;background:var(--border);border-radius:4px;overflow:hidden}.mastery-fill{height:100%;border-radius:4px}.page{padding:16px 16px 80px}.page-title{font-size:20px;font-weight:700;margin-bottom:16px}.toast{position:fixed;bottom:72px;left:50%;transform:translate(-50%);background:#1f2937;color:#fff;padding:10px 20px;border-radius:8px;font-size:14px;z-index:200;animation:fadeup .2s ease}@keyframes fadeup{0%{opacity:0;transform:translate(-50%) translateY(8px)}}