:root {
  --primary: #1B3A5C;
  --primary-dark: #122B45;
  --primary-light: #2A5080;
  --accent: #C8963E;
  --accent-dark: #A87A2F;
  --secondary: #2E7D6F;
  --danger: #C0392B;
  --warning: #D4A017;
  --bg: #F4F5F7;
  --card: #ffffff;
  --text: #1A1A2E;
  --text-muted: #5F6B7A;
  --border: #DDE1E7;
  --radius: 10px;
  --shadow: 0 2px 8px rgba(27,58,92,0.08);
}

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

body {
  font-family: -apple-system, 'Segoe UI', 'Noto Sans TC', system-ui, sans-serif;
  background: var(--bg);
  color: var(--text);
  min-height: 100vh;
}

/* ── NAV ── */
nav {
  background: var(--primary);
  padding: 0 24px;
  display: flex;
  align-items: center;
  gap: 4px;
  height: 56px;
  box-shadow: 0 2px 12px rgba(27,58,92,0.25);
  flex-wrap: nowrap;
  overflow-x: auto;
  -webkit-overflow-scrolling: touch;
}

nav .logo {
  font-size: 1.15rem;
  font-weight: 800;
  color: var(--accent);
  text-decoration: none;
  margin-right: 18px;
  letter-spacing: 0.5px;
  white-space: nowrap;
  flex-shrink: 0;
}

nav a {
  color: rgba(255,255,255,0.75);
  text-decoration: none;
  padding: 6px 14px;
  border-radius: 6px;
  font-size: 0.88rem;
  font-weight: 500;
  transition: all 0.15s;
  white-space: nowrap;
  flex-shrink: 0;
}

nav a:hover, nav a.active {
  background: rgba(255,255,255,0.12);
  color: #fff;
}

/* ── LAYOUT ── */
.container {
  max-width: 1000px;
  margin: 0 auto;
  padding: 28px 20px;
}

h1 { font-size: 1.6rem; margin-bottom: 20px; }
h2 { font-size: 1.2rem; margin-bottom: 12px; }

/* ── CARDS ── */
.card {
  background: var(--card);
  border-radius: var(--radius);
  padding: 24px;
  box-shadow: var(--shadow);
  border: 1px solid var(--border);
}

.grid-2 { display: grid; grid-template-columns: 1fr 1fr; gap: 16px; }
.grid-3 { display: grid; grid-template-columns: 1fr 1fr 1fr; gap: 16px; }
.grid-4 { display: grid; grid-template-columns: repeat(4,1fr); gap: 16px; }

/* ── DASHBOARD STAT ── */
.stat-card {
  background: var(--card);
  border-radius: var(--radius);
  padding: 20px;
  box-shadow: var(--shadow);
  border: 1px solid var(--border);
  text-align: center;
}
.stat-card .num { font-size: 2.2rem; font-weight: 700; color: var(--primary); }
.stat-card .label { font-size: 0.85rem; color: var(--text-muted); margin-top: 4px; }

/* ── BUTTONS ── */
.btn {
  display: inline-flex; align-items: center; justify-content: center;
  gap: 6px;
  padding: 10px 20px;
  border-radius: 8px;
  border: none;
  cursor: pointer;
  font-size: 0.9rem;
  font-weight: 600;
  transition: all 0.15s;
  text-decoration: none;
}

.btn-primary { background: var(--accent); color: #fff; }
.btn-primary:hover { background: var(--accent-dark); }
.btn-secondary { background: var(--secondary); color: #fff; }
.btn-secondary:hover { background: #236B5F; }
.btn-outline { background: transparent; color: var(--primary); border: 2px solid var(--primary); }
.btn-outline:hover { background: var(--primary); color: #fff; }
.btn-danger { background: var(--danger); color: #fff; }
.btn-lg { padding: 14px 32px; font-size: 1rem; }
.btn-sm { padding: 6px 14px; font-size: 0.82rem; }

/* ── PROGRESS BAR ── */
.progress-wrap { background: #DDE1E7; border-radius: 99px; height: 10px; overflow: hidden; }
.progress-bar { height: 100%; border-radius: 99px; transition: width 0.4s; }
.progress-bar.blue { background: var(--primary); }
.progress-bar.green { background: var(--secondary); }
.progress-bar.orange { background: var(--warning); }

/* ── FLASHCARD ── */
.flashcard-wrap {
  perspective: 1000px;
  width: 100%;
  max-width: 540px;
  margin: 0 auto;
  height: 280px;
  cursor: pointer;
}
.flashcard {
  width: 100%; height: 100%;
  position: relative;
  transform-style: preserve-3d;
  transition: transform 0.5s;
}
.flashcard.flipped { transform: rotateY(180deg); }
.flashcard-front, .flashcard-back {
  position: absolute; inset: 0;
  border-radius: var(--radius);
  backface-visibility: hidden;
  display: flex; flex-direction: column;
  align-items: center; justify-content: center;
  padding: 32px;
  box-shadow: var(--shadow);
  border: 1px solid var(--border);
}
.flashcard-front { background: var(--primary); color: #fff; }
.flashcard-back { background: var(--card); transform: rotateY(180deg); }
.flashcard-front .word { font-size: 2rem; font-weight: 700; }
.flashcard-front .part { font-size: 0.85rem; opacity: 0.75; margin-top: 6px; }
.flashcard-back .meaning { font-size: 1.3rem; font-weight: 600; text-align: center; }
.flashcard-back .example { font-size: 0.85rem; color: var(--text-muted); margin-top: 10px; text-align: center; font-style: italic; }

/* ── QUIZ ── */
.quiz-option {
  display: block; width: 100%;
  padding: 14px 18px;
  border: 2px solid var(--border);
  border-radius: 10px;
  background: var(--card);
  cursor: pointer;
  font-size: 0.95rem;
  text-align: left;
  transition: all 0.15s;
  margin-bottom: 10px;
}
.quiz-option:hover { border-color: var(--primary); background: #EEF2F7; }
.quiz-option.correct { border-color: var(--secondary); background: #E8F5F1; color: #1A5C50; }
.quiz-option.wrong { border-color: var(--danger); background: #FDEAEA; color: #8B1A1A; }
.quiz-option:disabled { cursor: not-allowed; }

.quiz-question {
  font-size: 1.1rem;
  font-weight: 600;
  margin-bottom: 20px;
  line-height: 1.6;
}

/* ── READING ── */
.passage {
  background: #F7F8FA;
  border-left: 4px solid var(--accent);
  border-radius: 0 8px 8px 0;
  padding: 20px;
  font-size: 0.95rem;
  line-height: 1.8;
  margin-bottom: 24px;
}

/* ── TIMER ── */
.timer-display {
  font-size: 2rem;
  font-weight: 700;
  color: var(--primary);
  font-variant-numeric: tabular-nums;
}
.timer-display.warning { color: var(--warning); }
.timer-display.danger { color: var(--danger); animation: pulse 0.5s infinite alternate; }
@keyframes pulse { from { opacity: 1; } to { opacity: 0.5; } }

/* ── BADGE ── */
.badge {
  display: inline-flex; align-items: center;
  padding: 3px 10px; border-radius: 99px;
  font-size: 0.78rem; font-weight: 600;
}
.badge-blue { background: #E0E8F0; color: var(--primary); }
.badge-green { background: #D6EDE8; color: #1A5C50; }
.badge-orange { background: #F5ECDA; color: #8A6A1E; }
.badge-red { background: #F5DADA; color: #8B1A1A; }

/* ── RESULT ── */
.result-circle {
  width: 130px; height: 130px;
  border-radius: 50%;
  border: 8px solid var(--primary);
  display: flex; flex-direction: column;
  align-items: center; justify-content: center;
  margin: 0 auto 20px;
}
.result-circle .score { font-size: 2.2rem; font-weight: 700; color: var(--primary); }
.result-circle .total { font-size: 0.85rem; color: var(--text-muted); }

/* ── MISC ── */
.mt-4 { margin-top: 16px; }
.mt-6 { margin-top: 24px; }
.mt-8 { margin-top: 32px; }
.mb-4 { margin-bottom: 16px; }
.flex { display: flex; }
.flex-center { display: flex; align-items: center; justify-content: center; }
.gap-2 { gap: 8px; }
.gap-3 { gap: 12px; }
.gap-4 { gap: 16px; }
.text-center { text-align: center; }
.text-muted { color: var(--text-muted); font-size: 0.88rem; }
.hidden { display: none !important; }
.section-title { font-size: 0.8rem; font-weight: 700; text-transform: uppercase; letter-spacing: 1px; color: var(--text-muted); margin-bottom: 12px; }

/* ── WORD CATEGORY TABS ── */
.tabs { display: flex; gap: 8px; flex-wrap: wrap; margin-bottom: 20px; }
.tab {
  padding: 6px 16px; border-radius: 99px; border: 2px solid var(--border);
  background: var(--card); cursor: pointer; font-size: 0.85rem; font-weight: 500;
  transition: all 0.15s;
}
.tab.active { background: var(--primary); border-color: var(--primary); color: #fff; }

/* ── NOTIFICATION ── */
#notification {
  position: fixed; top: 72px; right: 20px; z-index: 999;
  padding: 12px 20px; border-radius: 10px;
  font-weight: 600; font-size: 0.9rem;
  box-shadow: 0 8px 24px rgba(0,0,0,0.12);
  transition: opacity 0.3s;
}
#notification.success { background: #D6EDE8; color: #1A5C50; }
#notification.error { background: #FDEAEA; color: #8B1A1A; }

/* ── RESPONSIVE ── */

/* Tablet */
@media (max-width: 768px) {
  .grid-4 { grid-template-columns: 1fr 1fr; }
  .flashcard-wrap { height: 240px; }
  .flashcard-front, .flashcard-back { padding: 24px; }
}

/* Mobile */
@media (max-width: 640px) {
  nav {
    padding: 0 12px;
    gap: 4px;
    height: 52px;
    overflow-x: auto;
    -webkit-overflow-scrolling: touch;
  }
  nav .logo { font-size: 1rem; margin-right: 8px; }
  nav a { padding: 5px 10px; font-size: 0.8rem; white-space: nowrap; }

  .container { padding: 16px 12px; }
  h1 { font-size: 1.3rem; margin-bottom: 14px; }

  .grid-2, .grid-3, .grid-4 { grid-template-columns: 1fr; }
  .card { padding: 16px; }

  .stat-card { padding: 14px; }
  .stat-card .num { font-size: 1.6rem; }
  .stat-card .label { font-size: 0.78rem; }

  .flashcard-wrap { height: 220px; max-width: 100%; }
  .flashcard-front .word { font-size: 1.5rem; }
  .flashcard-front, .flashcard-back { padding: 20px; }

  .btn-lg { padding: 12px 24px; font-size: 0.9rem; }
  .result-circle { width: 110px; height: 110px; }
  .result-circle .score { font-size: 1.8rem; }

  .passage { padding: 14px; font-size: 0.88rem; }
  .quiz-question { font-size: 1rem; }
  .quiz-option { padding: 12px 14px; font-size: 0.88rem; }
  .tabs { gap: 6px; }
  .tab { padding: 5px 12px; font-size: 0.8rem; }
}