:root {
  --primary: #4f46e5;
  --primary-dark: #4338ca;
  --bg: #f1f5f9;
  --card-bg: #ffffff;
  --text: #1e293b;
  --muted: #64748b;
  --border: #e2e8f0;
}

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

body {
  font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, sans-serif;
  background: var(--bg);
  color: var(--text);
  padding-bottom: 70px;
  -webkit-tap-highlight-color: transparent;
}

header {
  background: var(--primary);
  color: #fff;
  padding: 16px;
  text-align: center;
  position: sticky;
  top: 0;
  z-index: 10;
}
header h1 { font-size: 1.2rem; }

main { padding: 16px; max-width: 600px; margin: 0 auto; }

.tab { display: none; }
.tab.active { display: block; }

h2 { font-size: 1rem; margin: 16px 0 8px; color: var(--muted); }

/* Inputs & buttons */
input, form input {
  width: 100%;
  padding: 12px;
  border: 1px solid var(--border);
  border-radius: 10px;
  font-size: 1rem;
  margin-bottom: 8px;
  background: #fff;
}
input:focus { outline: 2px solid var(--primary); border-color: transparent; }

.btn-primary {
  background: var(--primary);
  color: #fff;
  border: none;
  padding: 12px 20px;
  border-radius: 10px;
  font-size: 1rem;
  font-weight: 600;
  cursor: pointer;
  width: 100%;
}
.btn-primary:active { background: var(--primary-dark); }

.btn-secondary {
  background: #fff;
  color: var(--primary);
  border: 1px solid var(--primary);
  padding: 10px 16px;
  border-radius: 10px;
  font-size: 0.95rem;
  font-weight: 600;
  cursor: pointer;
  width: 100%;
}
.btn-secondary:active { background: #eef2ff; }
.review-toolbar { display: flex; flex-direction: column; gap: 8px; margin-bottom: 8px; }

.row { display: flex; gap: 8px; }
.row input { flex: 1; margin-bottom: 0; }
.row .btn-primary { width: auto; white-space: nowrap; }

.muted { color: var(--muted); font-size: 0.85rem; margin: 8px 0; }
.hidden { display: none !important; }

/* Flashcard */
.card {
  background: var(--card-bg);
  border-radius: 16px;
  padding: 32px 20px;
  text-align: center;
  box-shadow: 0 4px 12px rgba(0,0,0,0.06);
  margin-top: 20px;
}
.card-progress { color: var(--muted); font-size: 0.8rem; margin-bottom: 16px; }
.card-word { font-size: 2.2rem; font-weight: 700; }
.card-phonetic { color: var(--muted); margin: 8px 0 24px; font-size: 1.1rem; }
.card-back { margin-top: 20px; border-top: 1px solid var(--border); padding-top: 20px; }
.fc-pos { color: var(--primary); font-weight: 600; }
.fc-meaning { font-size: 1.4rem; font-weight: 600; margin: 8px 0; }
.fc-example { font-style: italic; margin-top: 12px; }
.fc-example-vi { color: var(--muted); margin-top: 4px; }

.grade-buttons { display: grid; grid-template-columns: repeat(4, 1fr); gap: 8px; margin-top: 24px; }
.grade { padding: 14px 4px; border: none; border-radius: 10px; font-weight: 600; color: #fff; cursor: pointer; font-size: 0.9rem; }
.grade.again { background: #ef4444; }
.grade.hard  { background: #f59e0b; }
.grade.good  { background: #10b981; }
.grade.easy  { background: #3b82f6; }

.empty { text-align: center; padding: 60px 20px; }
.empty p { margin: 8px 0; font-size: 1.1rem; }

/* Word list */
.word-item {
  background: var(--card-bg);
  border-radius: 12px;
  padding: 14px 16px;
  margin-bottom: 8px;
  box-shadow: 0 1px 4px rgba(0,0,0,0.04);
}
.word-item .w-head { display: flex; justify-content: space-between; align-items: baseline; }
.word-item .w-word { font-weight: 700; font-size: 1.1rem; }
.word-item .w-phon { color: var(--muted); font-size: 0.85rem; margin-left: 8px; }
.word-item .w-meaning { margin-top: 4px; }
.word-item .w-example { font-style: italic; color: var(--muted); font-size: 0.85rem; margin-top: 6px; }
.word-item .w-del { background: none; border: none; color: #ef4444; cursor: pointer; font-size: 1.2rem; }
.w-due { font-size: 0.75rem; color: var(--muted); margin-top: 6px; }

/* Stats */
.stats-grid { display: grid; grid-template-columns: repeat(3, 1fr); gap: 12px; margin-top: 16px; }
.stat { background: var(--card-bg); border-radius: 12px; padding: 20px 8px; text-align: center; box-shadow: 0 1px 4px rgba(0,0,0,0.04); }
.stat-num { font-size: 2rem; font-weight: 700; color: var(--primary); }
.stat-label { color: var(--muted); font-size: 0.8rem; margin-top: 4px; }

/* Tab bar */
#tabbar {
  position: fixed;
  bottom: 0; left: 0; right: 0;
  display: flex;
  background: #fff;
  border-top: 1px solid var(--border);
  padding-bottom: env(safe-area-inset-bottom);
}
#tabbar button {
  flex: 1;
  background: none;
  border: none;
  padding: 12px 4px;
  font-size: 0.75rem;
  color: var(--muted);
  cursor: pointer;
}
#tabbar button.active { color: var(--primary); font-weight: 600; }