:root{
  --bg:#0b1220;
  --panel:#0f1a2f;
  --card:#0d1628;
  --text:#e7eefc;
  --muted:#a9b7d1;
  --line:rgba(255,255,255,.10);
  --accent:#6ee7ff;
  --good:#66ffb3;
  --bad:#ff6b9a;
  --warn:#ffd166;
}
*{box-sizing:border-box}
body{
  margin:0;
  font-family: ui-sans-serif, system-ui, -apple-system, Segoe UI, Roboto, "Noto Sans TC", "PingFang TC", "Microsoft JhengHei", sans-serif;
  background:radial-gradient(1200px 800px at 20% -10%, rgba(110,231,255,.18), transparent 60%),
             radial-gradient(900px 700px at 100% 0%, rgba(255,107,154,.12), transparent 60%),
             var(--bg);
  color:var(--text);
}
.topbar{
  position:sticky; top:0; z-index:10;
  display:flex; justify-content:space-between; align-items:center;
  padding:14px 16px;
  border-bottom:1px solid var(--line);
  backdrop-filter: blur(12px);
  background:rgba(11,18,32,.75);
}
.brand{display:flex; gap:12px; align-items:center}
.logo{
  width:44px; height:44px;
  border-radius:14px;
  display:grid; place-items:center;
  background:linear-gradient(135deg, rgba(110,231,255,.25), rgba(255,107,154,.18));
  border:1px solid var(--line);
  font-weight:800;
  letter-spacing:.5px;
}
.title{font-size:16px; font-weight:800}
.subtitle{font-size:12px; color:var(--muted); margin-top:2px}
.top-actions{display:flex; gap:10px; align-items:center}
.link{color:var(--accent); text-decoration:none}
.link:hover{text-decoration:underline}
.container{max-width:1040px; margin:18px auto; padding:0 14px}
.panel{
  background:linear-gradient(180deg, rgba(255,255,255,.04), rgba(255,255,255,.02));
  border:1px solid var(--line);
  border-radius:18px;
  padding:16px;
  box-shadow: 0 12px 40px rgba(0,0,0,.25);
}
.row{display:flex; gap:14px; align-items:flex-start}
.wrap{flex-wrap:wrap}
.field{min-width:220px}
.field.grow{flex:1}
label{display:block; font-size:12px; color:var(--muted); margin:2px 0 6px}
select{
  width:100%;
  padding:10px 12px;
  border-radius:12px;
  border:1px solid var(--line);
  background:rgba(13,22,40,.8);
  color:var(--text);
  outline:none;
}
.hint{font-size:12px; color:var(--muted); margin-top:6px; line-height:1.45}
.stats{
  margin-top:14px;
  display:grid;
  grid-template-columns:repeat(4, 1fr);
  gap:10px;
}
.stat{
  background:rgba(13,22,40,.65);
  border:1px solid var(--line);
  border-radius:14px;
  padding:10px 12px;
}
.stat-k{font-size:18px; font-weight:900}
.stat-v{font-size:12px; color:var(--muted); margin-top:2px}
.toolbar{display:flex; gap:10px; flex-wrap:wrap; margin:14px 0 10px}
.btn{
  padding:10px 12px;
  border-radius:12px;
  border:1px solid var(--line);
  background:rgba(13,22,40,.65);
  color:var(--text);
  cursor:pointer;
}
.btn:hover{border-color:rgba(255,255,255,.22)}
.btn.primary{background:linear-gradient(135deg, rgba(110,231,255,.22), rgba(255,107,154,.18))}
.btn.ghost{background:transparent}
.seg{display:flex; border:1px solid var(--line); border-radius:14px; overflow:hidden; width:100%}
.seg-btn{
  flex:1;
  padding:10px 10px;
  background:transparent;
  border:0;
  color:var(--muted);
  cursor:pointer;
}
.seg-btn.active{background:rgba(110,231,255,.12); color:var(--text)}
#quiz{margin-top:10px}
.card{
  background:rgba(13,22,40,.65);
  border:1px solid var(--line);
  border-radius:16px;
  padding:14px;
}
.qhead{display:flex; justify-content:space-between; gap:10px; align-items:center}
.qno{font-weight:900}
.badge{
  font-size:12px;
  padding:4px 8px;
  border-radius:999px;
  border:1px solid var(--line);
  color:var(--muted);
}
.badge.medium{color:var(--accent)}
.badge.hard{color:var(--warn)}
.qtext{margin:10px 0 12px; line-height:1.6}
.options{display:grid; gap:8px}
.opt{
  display:flex; gap:10px; align-items:flex-start;
  padding:10px 12px;
  border-radius:14px;
  border:1px solid var(--line);
  cursor:pointer;
}
.opt input{margin-top:3px}
.opt:hover{border-color:rgba(255,255,255,.22)}
.opt.correct{border-color:rgba(102,255,179,.6); background:rgba(102,255,179,.08)}
.opt.wrong{border-color:rgba(255,107,154,.65); background:rgba(255,107,154,.08)}
.feedback{margin-top:12px; border-top:1px dashed var(--line); padding-top:12px}
.feedback .row2{display:flex; gap:10px; flex-wrap:wrap; align-items:center}
.pill{
  font-size:12px;
  padding:5px 10px;
  border-radius:999px;
  border:1px solid var(--line);
}
.pill.good{border-color:rgba(102,255,179,.6); color:var(--good)}
.pill.bad{border-color:rgba(255,107,154,.65); color:var(--bad)}
.explain{color:var(--text); line-height:1.6; margin-top:10px}
.extra{color:var(--muted); line-height:1.6; margin-top:10px}
.small{font-size:12px; color:var(--muted)}
.footer{margin-top:16px}
.summary{margin-top:12px}
.hidden{display:none}
.prose{line-height:1.8}
.prose h2{margin:14px 0 6px}
.prose ul,.prose ol{margin-top:6px}
@media (max-width:760px){
  .stats{grid-template-columns:repeat(2, 1fr)}
}