:root {
  --bg: #0f1115;
  --card: #1a1d24;
  --card-border: #2a2e38;
  --text: #e8e9ec;
  --text-dim: #9aa0ac;
  --accent: #4f8cff;
  --accent-dim: #2d4f8f;
  --good: #3ecf8e;
  --bad: #ff6b6b;
  --warn: #f5a623;
  --radius: 12px;
}

@media (prefers-color-scheme: light) {
  :root {
    --bg: #f4f5f7;
    --card: #ffffff;
    --card-border: #e2e4e9;
    --text: #1b1d22;
    --text-dim: #6b7280;
    --accent: #3366ff;
    --accent-dim: #dbe4ff;
  }
}

* { box-sizing: border-box; }

body {
  margin: 0;
  font-family: -apple-system, BlinkMacSystemFont, "Hiragino Sans", "Yu Gothic", sans-serif;
  background: var(--bg);
  color: var(--text);
  line-height: 1.7;
}

#app {
  max-width: 640px;
  margin: 0 auto;
  padding: 0 16px 60px;
}

.app-header {
  padding: 20px 0 12px;
  position: sticky;
  top: 0;
  background: var(--bg);
  z-index: 10;
}

.app-header h1 {
  font-size: 1.3rem;
  margin: 0 0 12px;
}

.overall-progress {
  display: flex;
  align-items: center;
  gap: 10px;
}

.overall-progress-bar {
  flex: 1;
  height: 8px;
  border-radius: 4px;
  background: var(--card-border);
  overflow: hidden;
}

.overall-progress-fill {
  height: 100%;
  background: var(--accent);
  width: 0%;
  transition: width 0.3s ease;
}

.overall-progress-text {
  font-size: 0.8rem;
  color: var(--text-dim);
  white-space: nowrap;
}

/* ── Tier section ── */
.tier-section { margin-top: 24px; }
.tier-title {
  font-size: 1.05rem;
  font-weight: 700;
  margin-bottom: 10px;
  display: flex;
  align-items: center;
  gap: 8px;
}
.tier-badge {
  font-size: 0.7rem;
  padding: 2px 8px;
  border-radius: 999px;
  background: var(--accent-dim);
  color: var(--accent);
  font-weight: 600;
}

.lesson-card {
  background: var(--card);
  border: 1px solid var(--card-border);
  border-radius: var(--radius);
  padding: 14px 16px;
  margin-bottom: 10px;
  display: flex;
  align-items: center;
  gap: 12px;
}

.lesson-status {
  width: 28px;
  height: 28px;
  border-radius: 50%;
  flex-shrink: 0;
  display: flex;
  align-items: center;
  justify-content: center;
  font-size: 0.85rem;
  font-weight: 700;
  background: var(--card-border);
  color: var(--text-dim);
}
.lesson-status.done {
  background: var(--good);
  color: #06301e;
}

.lesson-info { flex: 1; min-width: 0; }
.lesson-title { font-weight: 600; font-size: 0.95rem; }
.lesson-summary { font-size: 0.8rem; color: var(--text-dim); margin-top: 2px; }
.lesson-score { font-size: 0.75rem; color: var(--text-dim); margin-top: 4px; }

.lesson-actions {
  display: flex;
  flex-direction: column;
  gap: 6px;
  flex-shrink: 0;
}

button {
  font-family: inherit;
  cursor: pointer;
  border: none;
  border-radius: 8px;
  padding: 8px 14px;
  font-size: 0.82rem;
  font-weight: 600;
  transition: opacity 0.15s;
}
button:active { opacity: 0.7; }

.btn-primary { background: var(--accent); color: #fff; }
.btn-secondary { background: var(--card-border); color: var(--text); }
.btn-full { width: 100%; }

/* ── Lesson reading view ── */
.lesson-view { padding-top: 8px; }
.back-link {
  background: none;
  color: var(--accent);
  padding: 4px 0;
  font-size: 0.85rem;
  margin-bottom: 12px;
}
.lesson-view h2 { font-size: 1.25rem; margin: 0 0 20px; }

.section-block {
  background: var(--card);
  border: 1px solid var(--card-border);
  border-radius: var(--radius);
  padding: 16px;
  margin-bottom: 12px;
}
.section-block h3 { font-size: 1rem; margin: 0 0 8px; color: var(--accent); }
.section-block p { margin: 0; font-size: 0.92rem; color: var(--text); }

.lesson-footer { margin-top: 20px; }

/* ── Quiz view ── */
.quiz-progress {
  font-size: 0.8rem;
  color: var(--text-dim);
  margin-bottom: 10px;
}
.quiz-question {
  font-size: 1.05rem;
  font-weight: 600;
  margin-bottom: 16px;
}
.quiz-choice {
  display: block;
  width: 100%;
  text-align: left;
  background: var(--card);
  border: 1px solid var(--card-border);
  border-radius: var(--radius);
  padding: 14px 16px;
  margin-bottom: 10px;
  font-size: 0.92rem;
  color: var(--text);
  font-weight: 500;
}
.quiz-choice:disabled { cursor: default; }
.quiz-choice.correct { background: rgba(62,207,142,0.15); border-color: var(--good); }
.quiz-choice.incorrect { background: rgba(255,107,107,0.15); border-color: var(--bad); }

.quiz-explanation {
  background: var(--card);
  border: 1px solid var(--card-border);
  border-left: 3px solid var(--accent);
  border-radius: 8px;
  padding: 12px 14px;
  font-size: 0.88rem;
  color: var(--text-dim);
  margin: 14px 0;
}

.quiz-result {
  text-align: center;
  padding: 30px 16px;
}
.quiz-result .score {
  font-size: 2.4rem;
  font-weight: 800;
  color: var(--accent);
  margin: 10px 0;
}
.quiz-result .score-label { color: var(--text-dim); font-size: 0.85rem; }