:root{
  --blue:#2563eb;--blue-dark:#1d4ed8;--bg:#f8fafc;--card:#ffffff;--text:#0f172a;--muted:#64748b;--border:#e2e8f0;--green:#16a34a;--red:#dc2626;--amber:#d97706;
  --shadow:0 12px 30px rgba(15,23,42,.08);
}
*{box-sizing:border-box}
body{margin:0;font-family:-apple-system,BlinkMacSystemFont,"Segoe UI",Roboto,"Noto Sans SC","PingFang SC","Microsoft YaHei",Arial,sans-serif;background:var(--bg);color:var(--text);}
button,input,select{font:inherit}
.app-shell{max-width:760px;margin:0 auto;min-height:100vh;padding:14px 14px 86px}
.header{position:sticky;top:0;z-index:5;background:rgba(248,250,252,.92);backdrop-filter:blur(10px);padding:10px 0 12px;display:flex;align-items:center;justify-content:space-between;gap:10px}
.brand{display:flex;align-items:center;gap:10px}.logo{width:42px;height:42px;border-radius:14px;background:linear-gradient(135deg,#2563eb,#60a5fa);color:#fff;display:grid;place-items:center;font-weight:800;box-shadow:var(--shadow)}
h1{font-size:22px;margin:0}.subtitle{color:var(--muted);font-size:13px;margin-top:2px}.pill{background:#dbeafe;color:#1e40af;border-radius:999px;padding:7px 10px;font-weight:700;font-size:12px;white-space:nowrap}
.card{background:var(--card);border:1px solid var(--border);border-radius:22px;padding:16px;margin:12px 0;box-shadow:var(--shadow)}
.grid{display:grid;grid-template-columns:repeat(2,minmax(0,1fr));gap:12px}.grid-3{display:grid;grid-template-columns:repeat(3,minmax(0,1fr));gap:10px}
.stat{background:#fff;border:1px solid var(--border);border-radius:18px;padding:14px;text-align:center}.stat b{display:block;font-size:22px}.stat span{color:var(--muted);font-size:12px}.muted{color:var(--muted)}
.btn{border:0;border-radius:16px;padding:13px 14px;background:var(--blue);color:#fff;font-weight:800;cursor:pointer;text-decoration:none;display:inline-flex;align-items:center;justify-content:center;gap:8px;min-height:48px}.btn:active{transform:scale(.99)}.btn.secondary{background:#e2e8f0;color:#0f172a}.btn.ghost{background:#fff;color:var(--blue);border:1px solid #bfdbfe}.btn.red{background:var(--red)}.btn.green{background:var(--green)}.btn.amber{background:var(--amber)}.btn.full{width:100%}
.list{display:flex;flex-direction:column;gap:10px}.row{display:flex;justify-content:space-between;align-items:center;gap:12px;border:1px solid var(--border);background:#fff;border-radius:18px;padding:14px;text-decoration:none;color:inherit}.row:hover{border-color:#bfdbfe}.row-title{font-weight:800}.row-sub{font-size:13px;color:var(--muted);margin-top:4px}.badge{border-radius:999px;background:#f1f5f9;color:#334155;padding:5px 8px;font-size:12px;font-weight:700;white-space:nowrap}
.question-it{font-size:22px;line-height:1.45;font-weight:800;margin:10px 0 8px}.question-zh{font-size:17px;line-height:1.55;color:#334155;background:#f8fafc;border:1px dashed var(--border);border-radius:16px;padding:12px;margin-top:12px}.answer-grid{display:grid;grid-template-columns:1fr 1fr;gap:12px;margin-top:14px}.answer-btn{font-size:20px;padding:18px;border-radius:18px;border:2px solid var(--border);background:#fff;font-weight:900}.answer-btn.selected,.answer-btn:hover{border-color:var(--blue);background:#eff6ff}.answer-btn.correct{border-color:#86efac;background:#dcfce7;color:#166534}.answer-btn.wrong{border-color:#fecaca;background:#fee2e2;color:#991b1b}.explanation{border-left:5px solid var(--blue);background:#eff6ff;border-radius:16px;padding:14px;margin-top:14px;line-height:1.65}.keyword{display:inline-block;margin:4px 6px 0 0;padding:6px 9px;background:#f1f5f9;border-radius:999px;font-size:12px;color:#334155}
.bottom-nav{position:fixed;left:50%;transform:translateX(-50%);bottom:0;width:min(760px,100%);background:rgba(255,255,255,.95);backdrop-filter:blur(12px);border-top:1px solid var(--border);display:grid;grid-template-columns:repeat(5,1fr);padding:7px 6px calc(7px + env(safe-area-inset-bottom));z-index:10}.nav-item{padding:7px 4px;text-align:center;text-decoration:none;color:#64748b;border-radius:14px;font-size:12px;font-weight:700}.nav-item.active{background:#dbeafe;color:#1d4ed8}.nav-icon{display:block;font-size:20px;margin-bottom:2px}
.progress-bar{height:10px;background:#e2e8f0;border-radius:999px;overflow:hidden}.progress-fill{height:100%;background:var(--blue);border-radius:999px}.top-actions{display:flex;gap:8px;flex-wrap:wrap}.small{font-size:13px}.timer{font-variant-numeric:tabular-nums;font-weight:900;color:#1e40af}.danger{color:var(--red)}.success{color:var(--green)}
.search{width:100%;padding:13px 14px;border:1px solid var(--border);border-radius:16px;background:#fff;margin:8px 0 12px}.empty{text-align:center;padding:34px 20px;color:var(--muted)}.loading{padding:40px;text-align:center;color:var(--muted)}
@media(max-width:430px){.app-shell{padding:10px 10px 82px}.grid{grid-template-columns:1fr}.question-it{font-size:20px}.card{border-radius:18px;padding:14px}.header{align-items:flex-start}.pill{display:none}.answer-grid{grid-template-columns:1fr}.grid-3{grid-template-columns:repeat(3,1fr)}}

/* v2 updates: bilingual knowledge rules + image questions */
.image-wrap{display:flex;justify-content:center;margin:14px 0 12px;padding:14px;border:1px solid var(--border);border-radius:18px;background:#fff}
.question-image{width:min(220px,70vw);height:auto;display:block}
.mini-sign{width:54px;height:54px;object-fit:contain;float:left;margin:0 12px 6px 0;padding:6px;border:1px solid var(--border);border-radius:12px;background:#fff}
.rule-it{font-weight:700;color:#172033;margin-bottom:5px;line-height:1.45}
.rule-zh{color:#475569;line-height:1.55}
ol li{margin-bottom:12px}

/* v5 official image support */

.image-wrap{background:#fff;border:1px solid var(--border);border-radius:20px;padding:14px;margin:14px auto;text-align:center;box-shadow:0 8px 22px rgba(15,23,42,.06)}
.question-image{max-width:240px;width:min(70vw,240px);height:auto;display:block;margin:0 auto;border-radius:12px}
.image-caption{font-size:12px;color:var(--muted);margin-top:8px}
.mini-sign{width:64px;height:auto;display:block;margin:0 0 8px;border-radius:8px;border:1px solid var(--border);background:#fff}
@media (max-width:520px){.question-image{max-width:210px}.question-it{font-size:20px}}