:root {
  --bg: #f8f7f4;
  --surface: #ffffff;
  --border: #e2e0db;
  --text: #1a1a1a;
  --text-muted: #6b6860;
  --accent: #2563eb;
  --accent-hover: #1d4ed8;
  --green: #16a34a;
  --red: #dc2626;
  --radius: 12px;
  --shadow: 0 2px 8px rgba(0,0,0,0.08);
}

* { box-sizing: border-box; margin: 0; padding: 0; }

body {
  font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", sans-serif;
  background: var(--bg);
  color: var(--text);
  min-height: 100vh;
  padding: 16px;
}

/* ── Header ── */
#header {
  max-width: 720px;
  margin: 0 auto 20px;
  display: flex;
  align-items: center;
  justify-content: space-between;
  flex-wrap: wrap;
  gap: 10px;
}

#header h1 {
  font-size: 1.3rem;
  font-weight: 700;
  letter-spacing: -0.02em;
}

#stats {
  display: flex;
  gap: 16px;
  align-items: center;
  font-size: 0.9rem;
}

.stat { display: flex; align-items: center; gap: 5px; }
.stat-label { color: var(--text-muted); }
.stat-val { font-weight: 600; }
#streak-val { color: #d97706; }
#score-val { color: var(--green); }

#reset-btn {
  background: none;
  border: 1px solid var(--border);
  border-radius: 6px;
  padding: 4px 10px;
  font-size: 0.8rem;
  color: var(--text-muted);
  cursor: pointer;
}
#reset-btn:hover { background: var(--border); }

/* ── Mode tabs ── */
#mode-bar {
  max-width: 720px;
  margin: 0 auto 16px;
  display: flex;
  gap: 6px;
  flex-wrap: wrap;
}

.mode-btn {
  padding: 7px 16px;
  border-radius: 20px;
  border: 1.5px solid var(--border);
  background: var(--surface);
  font-size: 0.9rem;
  cursor: pointer;
  transition: all 0.15s;
}
.mode-btn:hover { border-color: var(--accent); color: var(--accent); }
.mode-btn.active {
  background: var(--accent);
  border-color: var(--accent);
  color: #fff;
  font-weight: 600;
}

/* ── Filter bar ── */
#filter-bar {
  max-width: 720px;
  margin: 0 auto 18px;
  display: flex;
  gap: 6px;
  flex-wrap: wrap;
  align-items: center;
}

#filter-bar label {
  font-size: 0.8rem;
  color: var(--text-muted);
  margin-right: 2px;
}

.filter-chip {
  padding: 4px 12px;
  border-radius: 16px;
  border: 1px solid var(--border);
  background: var(--surface);
  font-size: 0.78rem;
  cursor: pointer;
  transition: all 0.12s;
}
.filter-chip:hover { border-color: var(--accent); }
.filter-chip.active {
  background: #eff6ff;
  border-color: var(--accent);
  color: var(--accent);
  font-weight: 600;
}

/* ── Main card area ── */
#main {
  max-width: 720px;
  margin: 0 auto;
}

/* ── Progress bar ── */
#progress-wrap {
  height: 5px;
  background: var(--border);
  border-radius: 3px;
  margin-bottom: 18px;
  overflow: hidden;
}
#progress-bar {
  height: 100%;
  background: var(--accent);
  border-radius: 3px;
  transition: width 0.3s ease;
}

/* ── Card ── */
.card {
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  box-shadow: var(--shadow);
  padding: 36px 32px 28px;
  text-align: center;
  min-height: 260px;
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: center;
  gap: 12px;
}

.card-direction {
  font-size: 0.75rem;
  color: var(--text-muted);
  text-transform: uppercase;
  letter-spacing: 0.06em;
  align-self: flex-start;
}

.card-dev {
  font-size: 2.8rem;
  font-weight: 700;
  line-height: 1.2;
  letter-spacing: 0.02em;
}

.card-eng {
  font-size: 1.5rem;
  font-weight: 600;
  color: var(--text);
}

.card-rom {
  font-size: 1rem;
  color: var(--text-muted);
  font-style: italic;
  display: none;
}
.card-rom.visible { display: block; }

.card-hint {
  font-size: 0.82rem;
  color: var(--text-muted);
  margin-top: 4px;
}

/* pronunciation toggle */
.pron-toggle {
  display: inline-flex;
  align-items: center;
  gap: 5px;
  font-size: 0.75rem;
  font-weight: 500;
  color: #3b82f6;
  background: #eff6ff;
  border: 1px solid #bfdbfe;
  border-radius: 20px;
  padding: 3px 10px;
  cursor: pointer;
  transition: background 0.15s, border-color 0.15s;
  letter-spacing: 0.01em;
}
.pron-toggle:hover {
  background: #dbeafe;
  border-color: #93c5fd;
}

/* ── Answer section (flashcard) ── */
#answer-section { margin-top: 8px; width: 100%; }

.answer-box {
  background: #f0fdf4;
  border: 1px solid #bbf7d0;
  border-radius: 8px;
  padding: 16px 20px;
  margin-bottom: 12px;
  text-align: center;
}
.answer-box .ans-dev { font-size: 1.8rem; font-weight: 700; }
.answer-box .ans-eng { font-size: 1.1rem; color: var(--text-muted); margin-top: 4px; }

/* ── Buttons ── */
.btn {
  display: inline-flex;
  align-items: center;
  gap: 5px;
  padding: 10px 22px;
  border-radius: 8px;
  border: none;
  font-size: 0.95rem;
  font-weight: 600;
  cursor: pointer;
  transition: all 0.15s;
}

.btn-primary { background: var(--accent); color: #fff; }
.btn-primary:hover { background: var(--accent-hover); }

.btn-success { background: var(--green); color: #fff; }
.btn-success:hover { background: #15803d; }

.btn-danger { background: var(--red); color: #fff; }
.btn-danger:hover { background: #b91c1c; }

.btn-ghost {
  background: none;
  border: 1.5px solid var(--border);
  color: var(--text);
}
.btn-ghost:hover { background: var(--border); }

.btn-sm { padding: 6px 14px; font-size: 0.82rem; }

.btn-row {
  display: flex;
  gap: 10px;
  justify-content: center;
  flex-wrap: wrap;
  margin-top: 10px;
}

/* ── Reveal / show answer btn ── */
#reveal-btn { margin-top: 12px; }


/* ── Multiple choice ── */
#mc-options {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 10px;
  width: 100%;
  max-width: 480px;
  margin-top: 12px;
}

.mc-option {
  padding: 14px 12px;
  border: 1.5px solid var(--border);
  border-radius: 10px;
  background: var(--surface);
  font-size: 1rem;
  cursor: pointer;
  text-align: center;
  transition: all 0.15s;
  line-height: 1.3;
}
.mc-option:hover:not(:disabled) { border-color: var(--accent); background: #eff6ff; }
.mc-option.correct { border-color: var(--green); background: #f0fdf4; color: var(--green); font-weight: 700; }
.mc-option.wrong { border-color: var(--red); background: #fef2f2; color: var(--red); }
.mc-option:disabled { cursor: default; }

/* ── Explain button ── */
.explain-wrap {
  position: relative;
  display: inline-block;
  margin-top: 6px;
}

.explain-btn {
  background: none;
  border: 1px solid var(--border);
  border-radius: 6px;
  padding: 5px 12px;
  font-size: 0.78rem;
  color: var(--text-muted);
  cursor: pointer;
}
.explain-btn:hover { background: #eff6ff; color: var(--accent); border-color: var(--accent); }

.explain-tooltip {
  position: absolute;
  bottom: calc(100% + 6px);
  left: 50%;
  transform: translateX(-50%);
  background: #1a1a1a;
  color: #fff;
  font-size: 0.75rem;
  padding: 4px 10px;
  border-radius: 6px;
  white-space: nowrap;
  pointer-events: none;
  opacity: 0;
  transition: opacity 0.15s;
}
.explain-tooltip.show { opacity: 1; }

/* ── Empty state ── */
#empty-state {
  text-align: center;
  color: var(--text-muted);
  padding: 40px 20px;
}
#empty-state p { font-size: 1rem; }

/* ── Completion ── */
#completion {
  text-align: center;
  padding: 40px 20px;
}
#completion h2 { font-size: 1.4rem; margin-bottom: 8px; }
#completion p { color: var(--text-muted); margin-bottom: 20px; }

/* ── Responsive ── */
@media (max-width: 500px) {
  .card { padding: 28px 20px 22px; }
  .card-dev { font-size: 2.2rem; }
  #mc-options { grid-template-columns: 1fr; }
}