:root {
  --bg: #f6f7f4;
  --card: #ffffff;
  --ink: #1d2422;
  --muted: #5d6965;
  --brand: #0f5c4d;
  --brand-soft: #e3f1ed;
  --ok: #1f7a3a;
  --ok-soft: #e4f4e8;
  --bad: #b3261e;
  --bad-soft: #fbe9e7;
  --line: #dfe4e1;
  --accent: #d98a1c;
  --on-brand: #ffffff;
  --radius: 14px;
  --shadow: 0 1px 2px rgba(0,0,0,.05), 0 4px 14px rgba(0,0,0,.05);
}
@media (prefers-color-scheme: dark) {
  :root {
    --bg: #121615; --card: #1b2120; --ink: #e8eeec; --muted: #9aa7a3;
    --brand: #4fc3a6; --brand-soft: #18302b; --ok: #6fd38a; --ok-soft: #173123;
    --bad: #ff8a80; --bad-soft: #3a1c1a; --line: #2c3533; --on-brand: #0b1f1a; --accent: #f0b04d;
    --shadow: none;
  }
}
* { box-sizing: border-box; }
html, body { margin: 0; }
body {
  background: var(--bg); color: var(--ink);
  font-family: "Noto Sans Bengali", "Hind Siliguri", system-ui, -apple-system, "Segoe UI", sans-serif;
  font-size: 17px; line-height: 1.55;
}
button { font: inherit; color: inherit; }
a { color: var(--brand); }

.topbar {
  position: sticky; top: 0; z-index: 5;
  background: var(--card); border-bottom: 1px solid var(--line);
  padding: 10px 16px;
}
.brand { display: flex; align-items: center; gap: 10px; background: none; border: 0; cursor: pointer; padding: 0; text-align: left; }
.brand small { display: block; color: var(--muted); font-size: 13px; line-height: 1.2; }
.logo {
  width: 36px; height: 36px; border-radius: 10px; background: var(--brand); color: var(--on-brand);
  display: grid; place-items: center; font-weight: 800; font-size: 20px;
}

main { max-width: 720px; margin: 0 auto; padding: 16px; min-height: 70vh; }
.card { background: var(--card); border: 1px solid var(--line); border-radius: var(--radius); padding: 16px; margin-bottom: 14px; box-shadow: var(--shadow); }
h1 { font-size: 24px; margin: 4px 0 8px; line-height: 1.3; }
h2 { font-size: 19px; margin: 0 0 8px; }
.muted { color: var(--muted); font-size: 14px; }

.btn {
  display: block; width: 100%; text-align: left; cursor: pointer;
  background: var(--card); border: 1.5px solid var(--line); border-radius: 12px;
  padding: 14px 16px; margin: 8px 0; min-height: 52px;
}
.btn:hover { border-color: var(--brand); }
.btn.primary { background: var(--brand); border-color: var(--brand); color: var(--on-brand); text-align: center; font-weight: 700; }
.btn.ghost { text-align: center; }
.btn:disabled { opacity: .55; cursor: not-allowed; }
.row { display: flex; gap: 10px; }
.row .btn { flex: 1; }

.progress { height: 8px; background: var(--line); border-radius: 99px; overflow: hidden; margin-top: 8px; }
.progress > span { display: block; height: 100%; background: var(--brand); }

.section-btn { display: flex; justify-content: space-between; align-items: center; gap: 10px; }
.section-btn .en { display: block; color: var(--muted); font-size: 13px; }
.badge { font-size: 12px; padding: 3px 8px; border-radius: 99px; background: var(--brand-soft); color: var(--brand); white-space: nowrap; }
.badge.lock { background: var(--line); color: var(--muted); }

.qhead { display: flex; justify-content: space-between; align-items: center; color: var(--muted); font-size: 14px; margin-bottom: 6px; }
.qtext { font-size: 19px; font-weight: 600; margin: 6px 0 12px; font-family: system-ui, -apple-system, "Segoe UI", sans-serif; }
.opt { font-family: system-ui, -apple-system, "Segoe UI", sans-serif; }
.opt.correct { border-color: var(--ok); background: var(--ok-soft); }
.opt.wrong { border-color: var(--bad); background: var(--bad-soft); }
.opt.chosen { border-color: var(--brand); background: var(--brand-soft); }
.explain { border-left: 4px solid var(--brand); background: var(--brand-soft); padding: 12px 14px; border-radius: 0 12px 12px 0; margin-top: 12px; }
.explain .verdict { font-weight: 700; margin-bottom: 4px; }
.explain .verdict.ok { color: var(--ok); }
.explain .verdict.bad { color: var(--bad); }
.audio { margin-top: 10px; font-size: 14px; }
.audio .placeholder { display: inline-block; padding: 6px 10px; border: 1px dashed var(--muted); border-radius: 10px; color: var(--muted); }

.timer { font-variant-numeric: tabular-nums; font-weight: 700; color: var(--accent); }
.result-score { font-size: 44px; font-weight: 800; margin: 4px 0; }
.pass { color: var(--ok); } .fail { color: var(--bad); }

.unlock input {
  width: 100%; padding: 12px; border-radius: 10px; border: 1.5px solid var(--line);
  background: var(--bg); color: var(--ink); font: inherit; margin: 8px 0;
}
.msg { font-size: 14px; margin-top: 6px; }
.msg.ok { color: var(--ok); } .msg.bad { color: var(--bad); }

.foot { max-width: 720px; margin: 10px auto 30px; padding: 0 16px; font-size: 13px; color: var(--muted); }