/* ===== 全局 ===== */
*{margin:0;padding:0;box-sizing:border-box}
:root{
  --primary:#2563eb;--primary-dark:#1d4ed8;
  --success:#16a34a;--danger:#dc2626;--warning:#f59e0b;
  --bg:#f0f2f5;--card:#fff;--text:#1f2937;--text2:#6b7280;
  --border:#e5e7eb;--sidebar:#1a1a2e;
  --safe-bottom:env(safe-area-inset-bottom,0px);
}
html,body{height:100%;font-family:"PingFang SC","Microsoft YaHei",system-ui,sans-serif;background:var(--bg);color:var(--text);-webkit-tap-highlight-color:transparent}
body{padding-bottom:calc(60px + var(--safe-bottom))}
.hidden{display:none!important}

/* ===== 底部导航 ===== */
#bottom-nav{
  position:fixed;bottom:0;left:0;right:0;height:calc(60px + var(--safe-bottom));
  padding-bottom:var(--safe-bottom);
  background:var(--sidebar);display:flex;z-index:100;
  box-shadow:0 -2px 12px rgba(0,0,0,.15);
}
.nav-item{flex:1;display:flex;flex-direction:column;align-items:center;justify-content:center;color:#8899aa;font-size:10px;cursor:pointer;transition:.2s;padding:6px 0}
.nav-item.active{color:#60a5fa}
.nav-icon{font-size:22px;margin-bottom:2px}
.nav-label{font-size:11px}

/* ===== 页面 ===== */
.page{display:none;padding:16px 16px 24px;max-width:800px;margin:0 auto;min-height:calc(100vh - 60px)}
.page.active{display:block}

/* ===== 首页 ===== */
.header{text-align:center;padding:30px 0 20px}
.header h1{font-size:24px;color:var(--sidebar)}
.subtitle{color:var(--text2);margin-top:6px;font-size:14px}

.stats-grid{display:grid;grid-template-columns:1fr 1fr;gap:12px;margin-bottom:20px}
.stat-card{background:var(--card);border-radius:12px;padding:20px 16px;text-align:center;cursor:pointer;transition:.2s;box-shadow:0 1px 4px rgba(0,0,0,.06)}
.stat-card:active{transform:scale(.97)}
.stat-card.accent{background:linear-gradient(135deg,#fee2e2,#fecaca);border:1px solid #fca5a5}
.stat-num{font-size:32px;font-weight:700;color:var(--primary)}
.stat-card.accent .stat-num{color:var(--danger)}
.stat-label{font-size:14px;color:var(--text);margin-top:4px;font-weight:500}
.stat-sub{font-size:12px;color:var(--text2);margin-top:4px}

.progress-section{background:var(--card);border-radius:12px;padding:18px;margin-bottom:16px;box-shadow:0 1px 4px rgba(0,0,0,.06)}
.progress-section h3{font-size:15px;margin-bottom:10px}
.progress-bar-wrap{height:8px;background:#e5e7eb;border-radius:4px;overflow:hidden}
.progress-bar{height:100%;background:linear-gradient(90deg,var(--primary),#60a5fa);border-radius:4px;transition:width .5s}
.progress-text{font-size:12px;color:var(--text2);margin-top:8px}

.quick-actions{display:flex;gap:12px;margin-bottom:16px}
.quick-actions .btn-primary,.quick-actions .btn-outline{flex:1}

.reset-section{text-align:center;padding:10px 0}

/* ===== 按钮 ===== */
.btn-primary{background:var(--primary);color:#fff;border:none;border-radius:10px;padding:12px 24px;font-size:15px;font-weight:600;cursor:pointer;transition:.2s;width:auto}
.btn-primary:active{background:var(--primary-dark);transform:scale(.97)}
.btn-outline{background:#fff;color:var(--primary);border:1.5px solid var(--primary);border-radius:10px;padding:11px 24px;font-size:15px;font-weight:600;cursor:pointer;transition:.2s}
.btn-outline:active{background:#eff6ff}
.btn-danger{background:var(--danger);color:#fff;border:none;border-radius:10px;padding:12px 24px;font-size:15px;font-weight:600;cursor:pointer}
.btn-danger:active{opacity:.85}
.btn-danger-text{background:none;border:none;color:var(--danger);font-size:13px;cursor:pointer;padding:8px 16px}

/* ===== 选择题 ===== */
.page-header{display:flex;align-items:center;justify-content:space-between;margin-bottom:12px}
.page-header h2{font-size:20px}
.mode-switch{display:flex;gap:6px}
.mode-btn{padding:6px 16px;border-radius:8px;border:1.5px solid var(--border);background:#fff;color:var(--text2);font-size:13px;font-weight:500;cursor:pointer}
.mode-btn.active{background:var(--primary);color:#fff;border-color:var(--primary)}
.choice-progress{font-size:13px;color:var(--text2);margin-bottom:10px}

.card{background:var(--card);border-radius:14px;padding:20px;box-shadow:0 1px 6px rgba(0,0,0,.06);margin-bottom:16px}
.q-id{font-size:12px;color:var(--text2);margin-bottom:6px}
.q-text{font-size:15px;line-height:1.7;margin-bottom:16px;white-space:pre-wrap}

.opt-btn{display:block;width:100%;text-align:left;padding:14px 16px;margin-bottom:8px;border-radius:10px;border:1.5px solid var(--border);background:#fafafa;font-size:14px;line-height:1.5;cursor:pointer;transition:.15s;color:var(--text)}
.opt-btn:active{background:#f0f0f0}
.opt-btn.correct{background:#dcfce7;border-color:#86efac;color:#15803d}
.opt-btn.wrong{background:#fee2e2;border-color:#fca5a5;color:#dc2626}
.opt-btn.disabled{pointer-events:none;opacity:.85}

#choice-result{margin-top:12px}
#choice-result-text{font-size:15px;font-weight:600;margin-bottom:8px}
.explain-box{background:#f9fafb;border:1px solid var(--border);border-radius:10px;padding:14px;font-size:13px;line-height:1.7;color:#374151;white-space:pre-wrap}

.card-actions{display:flex;gap:10px;margin-top:16px;flex-wrap:wrap}
.card-actions .btn-primary,.card-actions .btn-outline,.card-actions .btn-danger{flex:1;min-width:120px;text-align:center}

/* ===== 列表 ===== */
.q-list{display:flex;flex-direction:column;gap:10px}
.q-list-item{background:var(--card);border-radius:12px;padding:16px;cursor:pointer;transition:.2s;box-shadow:0 1px 4px rgba(0,0,0,.05);display:flex;align-items:center;justify-content:space-between}
.q-list-item:active{transform:scale(.98)}
.q-list-item .title{font-size:15px;font-weight:500;flex:1}
.q-list-item .badge{font-size:11px;padding:3px 10px;border-radius:6px;white-space:nowrap;margin-left:10px}
.badge-done{background:#dcfce7;color:#15803d}
.badge-wrong{background:#fee2e2;color:#dc2626}
.badge-new{background:#e0e7ff;color:#3730a3}

.back-btn{background:none;border:none;color:var(--primary);font-size:14px;cursor:pointer;padding:4px 0;margin-bottom:12px;font-weight:500}
.toggle-btn{margin-bottom:12px;width:100%}
.answer-box{background:#f0fdf4;border:1px solid #bbf7d0;border-radius:10px;padding:16px;font-size:13px;line-height:1.8;white-space:pre-wrap;margin-bottom:12px}

/* ===== 错题集 ===== */
.wrong-tabs{display:flex;gap:6px;margin-bottom:14px}
.tab-btn{flex:1;padding:10px;border-radius:10px;border:1.5px solid var(--border);background:#fff;font-size:13px;font-weight:500;cursor:pointer;text-align:center;color:var(--text2)}
.tab-btn.active{background:var(--primary);color:#fff;border-color:var(--primary)}

.wrong-card{background:var(--card);border-radius:12px;padding:16px;margin-bottom:10px;box-shadow:0 1px 4px rgba(0,0,0,.05)}
.wrong-card .q-text{font-size:14px;margin-bottom:10px}
.wrong-card .streak{font-size:12px;color:var(--text2)}
.wrong-card .streak b{color:var(--primary)}

.empty-state{text-align:center;padding:60px 20px;color:var(--text2)}
.empty-state .emoji{font-size:48px;margin-bottom:12px}
.empty-state p{font-size:14px}

/* ===== Toast ===== */
.toast{position:fixed;top:50%;left:50%;transform:translate(-50%,-50%) scale(.9);background:rgba(0,0,0,.78);color:#fff;padding:12px 28px;border-radius:12px;font-size:14px;z-index:999;opacity:0;transition:.25s;pointer-events:none}
.toast.show{opacity:1;transform:translate(-50%,-50%) scale(1)}

/* ===== 响应式 ===== */
@media(min-width:600px){
  .stats-grid{grid-template-columns:repeat(4,1fr)}
  .page{padding:24px 24px 32px}
}