:root{
  --bg:#ffffff;
  --text:#0f172a;
  --muted:#475569;
  --border:#cbd5e1;
  --soft:#f8fafc;
  --accent:#2563eb;
  --good:#16a34a;
  --bad:#dc2626;
  --shadow: 0 10px 26px rgba(2,6,23,.08);
  --r:16px;
}
*{box-sizing:border-box}
html,body{height:100%}
body{
  margin:0;
  font-family:system-ui,-apple-system,Segoe UI,Roboto,Arial,sans-serif;
  background:var(--bg);
  color:var(--text);
}
a{color:inherit; text-decoration:none}
a:hover{text-decoration:underline}
.container{width:min(1000px,100%); margin:0 auto; padding:0 18px;}

.navbar{
  position:sticky; top:0; z-index:10;
  background:#fff;
  border-bottom:1px solid var(--border);
}
.navbar-inner{
  display:flex; align-items:center; justify-content:space-between;
  padding:12px 0; gap:14px;
}
.brand{display:flex; align-items:center; gap:12px; min-width: 210px;}
.brand img{
  width:44px; height:44px; border-radius:50%;
  border:1px solid var(--border);
  background:var(--soft);
  padding:6px;
}
.brand-title{display:flex; flex-direction:column; line-height:1.05;}
.brand-title .top{font-weight:900; font-size:16px}
.brand-title .sub{color:var(--muted); font-size:12px; font-weight:700}

.navlinks{
  display:flex; gap:16px; flex-wrap:wrap; justify-content:flex-end;
  font-weight:750; color:#334155;
}
.navlinks a{padding:8px 10px; border-radius:12px}
.navlinks a:hover{background:var(--soft); text-decoration:none}
.navlinks a.active{background:var(--soft); border:1px solid var(--border)}

.hero{padding:26px 0 10px;}
.hero h1{margin:0 0 10px; font-size:26px; letter-spacing:.2px}
.hero p{margin:0; color:var(--muted); line-height:1.6; max-width:76ch}

.card{
  background:#fff;
  border:1px solid var(--border);
  border-radius:var(--r);
  box-shadow:var(--shadow);
  overflow:hidden;
}
.card-header{
  padding:14px 16px;
  border-bottom:1px solid var(--border);
  background:linear-gradient(180deg,#fff 0%,#fbfdff 100%);
  display:flex; align-items:center; justify-content:space-between; gap:10px; flex-wrap:wrap;
}
.card-header .title{font-weight:900}
.pill{
  font-size:12px; color:var(--muted);
  border:1px solid var(--border);
  background:var(--soft);
  padding:7px 10px;
  border-radius:999px;
  white-space:nowrap;
}
.card-body{padding:16px}

.progress{
  height:10px; border-radius:999px;
  background:var(--soft);
  border:1px solid var(--border);
  overflow:hidden;
}
.bar{height:100%; width:0%; background:var(--accent); transition:width .25s ease;}

.question{font-size:18px; font-weight:900; margin:10px 0 12px; line-height:1.3;}
.meta{display:flex; gap:10px; flex-wrap:wrap; color:var(--muted); font-size:13px;}
.meta b{color:var(--text)}

.answers{
  display:grid;
  grid-template-columns: 1fr 1fr;
  gap:10px;
  margin:14px 0;
}
@media (max-width:600px){ .answers{grid-template-columns:1fr;} }

.answer-btn{
  width:100%;
  text-align:left;
  padding:12px 12px;
  border-radius:14px;
  border:1px solid var(--border);
  background:#fff;
  cursor:pointer;
  transition:transform .05s ease, background .12s ease, border-color .12s ease;
  font-weight:800;
}
.answer-btn:hover{background:#fcfdff; border-color:#cbd5e1}
.answer-btn:active{transform:scale(.99)}
.answer-btn[disabled]{opacity:.75; cursor:not-allowed}
.answer-btn.correct{border-color: rgba(22,163,74,.35); background: rgba(22,163,74,.08);}
.answer-btn.wrong{border-color: rgba(220,38,38,.35); background: rgba(220,38,38,.08);}

.explain{
  display:none;
  border:1px solid var(--border);
  background:var(--soft);
  border-radius:14px;
  padding:12px;
  color:var(--muted);
  font-size:13px;
  line-height:1.55;
}
.explain.show{display:block}

.actions{
  display:flex; gap:10px; justify-content:space-between; flex-wrap:wrap; margin-top:12px;
}
button.primary, button.secondary{
  border-radius:14px;
  padding:10px 12px;
  font-weight:900;
  cursor:pointer;
  border:1px solid transparent;
}
button.primary{background:var(--accent); color:#fff;}
button.primary:disabled{opacity:.55; cursor:not-allowed}
button.secondary{background:#fff; border-color:var(--border); color:var(--text);}

.note{margin-top:10px; color:var(--muted); font-size:13px; font-weight:800}