:root {
  --bg: #0f172a;
  --card: #1e293b;
  --border: #334155;
  --text: #e2e8f0;
  --muted: #94a3b8;
  --accent: #38bdf8;
  --accent-dark: #0ea5e9;
  --ok: #4ade80;
  --bad: #f87171;
  --warn: #fbbf24;
  --radius: 12px;
}

* { box-sizing: border-box; }

body {
  margin: 0;
  font-family: system-ui, -apple-system, Segoe UI, Roboto, sans-serif;
  background: var(--bg);
  color: var(--text);
  line-height: 1.5;
}

#app { max-width: 820px; margin: 0 auto; padding: 24px 16px 60px; }

header h1 {
  font-size: 1.6rem;
  margin: 0 0 12px;
  color: var(--accent);
}

.env-badge {
  display: inline-block;
  vertical-align: middle;
  margin-left: 10px;
  background: #b45309;
  color: #fff;
  font-size: 0.75rem;
  font-weight: 700;
  letter-spacing: 0.05em;
  padding: 3px 12px;
  border-radius: 999px;
}

.progress-strip {
  height: 6px;
  background: var(--border);
  border-radius: 999px;
  overflow: hidden;
  margin-bottom: 20px;
}

.screen { display: block; }
.screen[hidden] { display: none; }

.card {
  background: var(--card);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 22px;
  margin-bottom: 20px;
}

.card h2 { margin: 0 0 16px; font-size: 1.2rem; color: var(--accent); }

.field { margin-bottom: 18px; }
.field label { display: block; font-weight: 600; margin-bottom: 6px; }

.hint { color: var(--muted); font-size: 0.85rem; margin-top: 4px; font-weight: 400; }

.topic-select { display: flex; flex-wrap: wrap; gap: 8px; }
.topic-item {
  display: inline-flex;
  align-items: center;
  gap: 6px;
  border: 1px solid var(--border);
  border-radius: 999px;
  padding: 6px 14px;
  cursor: pointer;
  font-weight: 500;
}
.topic-item:hover { border-color: var(--accent); }
.topic-item input { accent-color: var(--accent); }

select, input[type=text] {
  background: var(--bg);
  color: var(--text);
  border: 1px solid var(--border);
  border-radius: 8px;
  padding: 10px 12px;
  font-size: 1rem;
  width: 100%;
}
select { max-width: 220px; }
input[type=text]:focus, select:focus { outline: none; border-color: var(--accent); }

button {
  border: 0;
  border-radius: 8px;
  padding: 11px 20px;
  font-size: 1rem;
  cursor: pointer;
  font-weight: 600;
}
button.primary { background: var(--accent-dark); color: #062033; }
button.primary:hover { background: var(--accent); }
button.primary:disabled { opacity: 0.5; cursor: not-allowed; }
button.secondary { background: var(--border); color: var(--text); margin-left: 8px; }
button.secondary:hover { background: var(--muted); }
button.small { padding: 6px 10px; font-size: 0.8rem; }
button.danger {
  background: transparent;
  color: var(--bad);
  border: 1px solid var(--bad);
  margin-top: 10px;
  font-size: 0.85rem;
  font-weight: 500;
}
button.danger:hover { background: rgba(248,113,113,0.12); }

/* quiz */
.quiz-top { display: flex; justify-content: space-between; align-items: center; margin-bottom: 12px; gap: 8px; }
.badge {
  background: var(--card);
  border: 1px solid var(--border);
  border-radius: 999px;
  padding: 4px 14px;
  font-size: 0.9rem;
}
.badge.correct-badge { color: var(--accent); border-color: var(--accent); }

.topic-tag {
  display: inline-block;
  font-size: 0.75rem;
  background: var(--bg);
  border-radius: 999px;
  padding: 2px 10px;
  color: var(--muted);
  margin: 0 0 12px;
}

.q-text {
  font-size: 1.05rem;
  margin: 0 0 16px;
  white-space: pre-wrap;
  word-break: break-word;
}

.q-area { margin-bottom: 16px; }

.mc-option {
  display: block;
  padding: 10px 12px;
  border: 1px solid var(--border);
  border-radius: 8px;
  margin-bottom: 8px;
  cursor: pointer;
}
.mc-option:hover { border-color: var(--accent); }
.mc-option input { margin-right: 8px; accent-color: var(--accent); }

.text-input { margin-bottom: 12px; }

.feedback {
  border-radius: 8px;
  padding: 12px 14px;
  margin-bottom: 14px;
}
.feedback.correct { background: rgba(74,222,128,0.12); border: 1px solid var(--ok); }
.feedback.wrong { background: rgba(248,113,113,0.12); border: 1px solid var(--bad); }
.feedback.partial { background: rgba(251,191,36,0.10); border: 1px solid var(--warn); }
.feedback .ok { color: var(--ok); font-weight: 700; }
.feedback .bad { color: var(--bad); font-weight: 700; }
.feedback .warn { color: var(--warn); font-weight: 700; }
.feedback .cor { color: var(--text); margin-top: 4px; }
.feedback .ans-break { color: var(--warn); margin-top: 4px; }

.actions { display: flex; gap: 10px; }

/* result */
.result { text-align: center; }
.result h2 { margin-top: 0; }
.score-big { font-size: 2.4rem; font-weight: 800; color: var(--accent); margin: 8px 0; }
.pass-threshold { color: var(--muted); }
.retake-notice {
  color: var(--warn);
  font-weight: 600;
  margin: 6px 0;
}
#retakeBox { margin: 8px 0; }
#retakeBox .primary { background: var(--warn); color: #1e293b; }
#retakeBox .primary:hover { background: #fcd34d; }

.stat-row {
  display: flex;
  justify-content: space-between;
  padding: 6px 0;
  border-bottom: 1px dashed var(--border);
}
.stat-row:last-child { border-bottom: 0; }
.pass-badge {
  color: var(--ok);
  font-size: 0.8rem;
  margin-left: 6px;
}

/* quiz history */
.history { margin-top: 14px; border-top: 1px solid var(--border); padding-top: 10px; }
.history h3 { margin: 0 0 6px; font-size: 1rem; color: var(--accent); }
.hist-item {
  display: flex;
  align-items: center;
  gap: 8px;
  padding: 7px 0;
  border-bottom: 1px dashed var(--border);
}
.hist-item:last-of-type { border-bottom: 0; }
.hist-replay {
  background: none;
  border: none;
  color: var(--accent);
  font-size: 0.9rem;
  text-align: left;
  cursor: pointer;
  padding: 0;
  flex: 1;
}
.hist-replay:hover { text-decoration: underline; }
.hist-meta { color: var(--muted); font-size: 0.8rem; white-space: nowrap; }
.hist-del {
  background: none;
  border: none;
  color: var(--bad);
  cursor: pointer;
  font-size: 0.95rem;
  padding: 0 4px;
}
.hist-del:hover { opacity: 0.7; }

.review-item {
  border: 1px solid var(--border);
  border-left: 4px solid var(--border);
  border-radius: 8px;
  padding: 14px;
  margin-bottom: 14px;
}
.review-item.correct { border-left-color: var(--ok); }
.review-item.wrong { border-left-color: var(--bad); }
.review-item.partial { border-left-color: var(--warn); background: rgba(251,191,36,0.05); }
.review-item .q-text { font-size: 0.95rem; margin: 6px 0; }
.review-item .answer-you { margin-top: 4px; }
.review-item .answer-correct { color: var(--ok); margin-top: 4px; }
.review-item.correct .answer-you { color: var(--ok); }
.review-item.wrong .answer-you { color: var(--bad); }
.review-item.partial .answer-you { color: var(--warn); }
.review-item .answer-break { color: var(--warn); margin-top: 2px; }
.review-count { font-size: 0.85rem; color: var(--muted); font-weight: 600; }
.credit {
  font-size: 0.75rem;
  font-weight: 700;
  padding: 1px 8px;
  border-radius: 999px;
  margin-left: 8px;
}
.credit-ok { color: var(--ok); border: 1px solid var(--ok); }
.credit-bad { color: var(--bad); border: 1px solid var(--bad); }
.credit-partial { color: var(--warn); border: 1px solid var(--warn); }

.exp-wrap { display: block; margin-top: 10px; }

/* explanation panel */
.expl {
  margin-top: 10px;
  padding: 10px 12px;
  background: var(--bg);
  border-left: 3px solid var(--accent);
  border-radius: 8px;
}
.expl .expl-details { margin-top: 6px; }
.expl .expl-details summary {
  cursor: pointer;
  color: var(--accent);
  font-size: 0.85rem;
  font-weight: 600;
  user-select: none;
}
.expl .expl-details summary:hover { text-decoration: underline; }
.expl .expl-details p {
  margin: 0 0 10px;
  font-size: 0.95rem;
  line-height: 1.6;
}
.expl .expl-details p:last-child { margin-bottom: 0; }
.expl .expl-ai-note {
  margin-top: 10px;
  padding-top: 8px;
  border-top: 1px dashed var(--border);
  font-size: 0.8rem;
  color: var(--muted);
  font-style: italic;
}
.expl-opts { list-style: none; margin: 0; padding: 0; }
.expl-opt { font-size: 0.9rem; margin: 4px 0; line-height: 1.4; }
.expl-opt.correct { color: var(--ok); }
.expl-opt.wrong { color: var(--text); }
.feedback .expl { margin-top: 12px; }

@media (max-width: 520px) {
  body { font-size: 0.95rem; }
  .card { padding: 16px; }
  .actions { flex-direction: column; }
  button.secondary { margin-left: 0; }
}