style.css

:root {
  --primary: #4361ee;
  --success: #06d6a0;
  --danger: #ef233c;
  --warning: #f8961e;
  --dark: #1a1a2e;
  --card-shadow: 0 6px 20px rgba(0,0,0,0.08);
}

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

body {
  font-family: 'Segoe UI', system-ui, sans-serif;
  line-height: 1.6;
  background: linear-gradient(135deg, #f5f7fa 0%, #e4edf5 100%);
  color: #333;
  padding: 20px;
  max-width: 1200px;
  margin: 0 auto;
  min-height: 100vh;
}

/* ── Header ── */
header { text-align: center; padding: 20px 12px 14px; position: relative; }
.header-top { display: flex; justify-content: center; align-items: center; gap: 12px; position: relative; }
h1 { font-size: 2.4rem; color: var(--dark); margin: 8px 0; }
.subtitle { color: #666; font-size: 1.05rem; margin: 4px 0 8px; }
header { position: relative; display: flex; align-items: center; justify-content: center; flex-wrap: wrap; padding: 0.8rem 1.2rem; text-align: center; }
.burger-group { position: static; display: inline-flex; align-items: center; gap: 8px; border: 1px solid rgba(67,97,238,0.25); border-radius: 14px; background: rgba(255,255,255,0.98); padding: 4px 10px; box-shadow: 0 4px 12px rgba(33,33,33,0.12); margin: 0 auto 8px; order: 0; }
.burger-btn {
  border: 0; border-radius: 10px; background: rgba(67,97,238,0.16);
  width: 40px; height: 40px; font-size: 1.1rem; line-height: 1; cursor: pointer;
  color: var(--primary); display: flex; align-items: center; justify-content: center;
  transition: transform 0.2s ease, background 0.2s ease, box-shadow 0.2s ease;
}
.burger-btn:hover { transform: translateY(-2px); background: rgba(67,97,238,0.34); box-shadow: 0 12px 24px rgba(67,97,238,0.26); }
.burger-btn:focus { outline: none; box-shadow: 0 0 0 3px rgba(67,97,238,0.25); }
.burger-label { font-size: 0.95rem; color: var(--primary); font-weight: 700; cursor: pointer; letter-spacing: 0.2px; }
.burger-lang-menu {
  position: absolute; top: 54px; left: 50%; transform: translateX(-50%); background: linear-gradient(180deg, #ffffff 0%, #f8faff 100%);
  border: 1px solid rgba(67,97,238,0.24); border-radius: 14px;
  box-shadow: 0 18px 28px rgba(23,45,93,0.18);
  display: flex; flex-direction: column; padding: 10px 8px; gap: 6px; width: 190px; z-index: 1000;
  transform-origin: top center; animation: popup 0.14s ease-out;
}
.burger-lang-menu::before { content: ""; position: absolute; top: -7px; right: 16px; width: 12px; height: 12px; background: #fff; border-top: 1px solid rgba(67,97,238,0.24); border-left: 1px solid rgba(67,97,238,0.24); transform: rotate(45deg); z-index: -1; }
.lang-option { border: 1px solid rgba(67,97,238,0.3); background: #fff; text-align: left; padding: 10px 14px; border-radius: 10px; cursor: pointer; color: #334475; font-weight: 600; transition: transform 0.15s ease, background 0.2s ease, border-color 0.2s ease;
}
.lang-option.active { background: rgba(67,97,238,0.2); border-color: rgba(67,97,238,0.75); color: #1f3f8a; box-shadow: 0 0 0 2px rgba(67,97,238,0.15); }
.lang-option:hover { background: rgba(67,97,238,0.18); transform: translateX(2px); border-color: rgba(67,97,238,0.7); }
@media (max-width: 760px) {
  header { align-items: center; padding-top: 4.2rem; }
  .burger-group { position: fixed; right: 0.8rem; top: 0.8rem; width: auto; max-width: 220px; }
  .burger-lang-menu { right: 0.2rem; left: auto; width: calc(100vw - 32px); max-width: 260px; }
  .subtitle { font-size: 0.95rem; }
  h1 { font-size: 1.8rem; }
}
@keyframes popup { from { opacity: 0; transform: scale(0.94); } to { opacity: 1; transform: scale(1); } }
.burger-lang-menu.hidden { display: none; }
.burger-menu-title { padding: 6px 12px; font-size: 0.85rem; color: #5f6b7b; text-transform: uppercase; letter-spacing: 0.5px; }
.lang-option { border: none; background: transparent; text-align: left; padding: 10px 12px;
  border-radius: 10px; cursor: pointer; color: #2b3a61; font-weight: 600; transition: all 0.2s;
}
.lang-option.active { background: rgba(67,97,238,0.12); color: var(--primary); }
.lang-option:hover { background: rgba(67,97,238,0.12); color: var(--primary); }

/* ── Mode Tabs ── */
.mode-tabs { display: flex; justify-content: center; gap: 10px; margin: 18px 0 10px; }
.tab-btn {
  padding: 10px 28px; border-radius: 50px; border: 2px solid #ddd;
  background: white; font-size: 1rem; font-weight: 600; cursor: pointer;
  transition: all 0.2s; color: #666;
}
.tab-btn.active { background: var(--primary); border-color: var(--primary); color: white; box-shadow: 0 4px 12px rgba(67,97,238,0.3); }
.tab-btn:hover:not(.active) { border-color: var(--primary); color: var(--primary); }

/* ── Controls ── */
.controls {
  display: flex; flex-wrap: wrap; gap: 10px;
  justify-content: center; align-items: center;
  margin: 8px 0;
}
.controls-actions { margin-top: 4px; }
select, input[type="text"] {
  padding: 10px 16px; border: 2px solid #ddd; border-radius: 50px;
  font-size: 0.95rem; background: white; transition: border-color 0.2s;
}
select:focus, input[type="text"]:focus { outline: none; border-color: var(--primary); }
input[type="text"] { min-width: 240px; }

/* ── Buttons ── */
.btn {
  background: var(--primary); color: white; border: none; padding: 10px 20px;
  border-radius: 50px; cursor: pointer; font-size: 0.95rem; font-weight: 600;
  transition: opacity 0.2s, transform 0.1s; white-space: nowrap;
}
.btn:hover { opacity: 0.88; transform: translateY(-1px); }
.btn-success { background: var(--success); }
.btn-danger  { background: var(--danger); }
.btn-export  { background: #6c757d !important; color: white !important; border-color: #6c757d !important; }
.btn-outline {
  background: white; color: var(--primary);
  border: 2px solid var(--primary);
}
.btn-outline:hover { background: var(--primary); color: white; }
.btn-outline.active { background: var(--primary); color: white; }

/* ── Stats / Progress ── */
.stats { background: white; border-radius: 16px; padding: 16px 22px; margin: 14px 0; box-shadow: var(--card-shadow); }
.stats-row { display: flex; align-items: center; justify-content: center; gap: 18px; flex-wrap: wrap; margin-bottom: 10px; font-size: 0.95rem; }
.stats-row strong { font-size: 1.1rem; color: var(--dark); }
.progress-track { background: #e9ecef; border-radius: 50px; height: 12px; overflow: hidden; }
.progress-fill { height: 100%; width: 0%; background: linear-gradient(90deg, var(--primary), var(--success)); border-radius: 50px; transition: width 0.5s ease; }
.progress-pct { text-align: center; font-size: 0.82rem; color: #888; margin-top: 5px; }

/* ── Word Grid ── */
.word-grid { display: grid; grid-template-columns: repeat(auto-fill, minmax(290px, 1fr)); gap: 22px; margin-top: 10px; }

/* ── Study Card ── */
.card {
  background: white; border-radius: 18px; box-shadow: var(--card-shadow);
  padding: 22px; transition: transform 0.25s ease, box-shadow 0.25s ease;
  border: 2px solid transparent;
}
.card:hover { transform: translateY(-4px); box-shadow: 0 12px 28px rgba(0,0,0,0.12); }
.card.is-mastered { border-color: var(--success); background: #f0fdf9; }

.card-header { display: flex; justify-content: space-between; align-items: flex-start; margin-bottom: 6px; }
.badges { display: flex; gap: 6px; flex-wrap: wrap; align-items: center; }

.level-badge { display: inline-block; padding: 3px 10px; border-radius: 20px; font-weight: 700; background: var(--primary); color: white; font-size: 0.8rem; }
.type-badge  { display: inline-block; padding: 3px 10px; border-radius: 20px; font-weight: 600; background: #f0f2ff; color: var(--primary); font-size: 0.78rem; border: 1px solid #d0d6ff; }
.sr-badge    { display: inline-block; padding: 3px 10px; border-radius: 20px; font-weight: 600; background: #fff3cd; color: #856404; font-size: 0.78rem; border: 1px solid #ffd060; }

.audio-btn {
  background: #f0f2ff; border: none; color: var(--primary);
  width: 36px; height: 36px; border-radius: 50%; cursor: pointer;
  display: flex; align-items: center; justify-content: center;
  transition: background 0.15s, transform 0.1s; flex-shrink: 0;
}
.audio-btn:hover { background: var(--primary); color: white; transform: scale(1.1); }

.chinese { font-size: 2.4rem; font-weight: bold; margin: 8px 0 4px; color: var(--dark); }
.pinyin  { font-size: 1.3rem; color: #e63946; margin: 4px 0; font-family: monospace; }
.meaning { font-size: 1.2rem; color: #1d3557; margin: 10px 0 6px; font-weight: 600; display: none; }

.sentence-block {
  background: #f8f9ff; border-left: 3px solid var(--primary);
  border-radius: 0 8px 8px 0; padding: 8px 12px; margin: 8px 0;
  font-size: 0.88rem; color: #444; display: none;
}
.sentence-zh { font-weight: 600; color: var(--dark); margin-bottom: 2px; }
.sentence-py { color: #e63946; font-family: monospace; font-size: 0.83rem; margin-bottom: 2px; }
.sentence-en { color: #555; font-style: italic; }

.card-actions { display: flex; gap: 8px; margin-top: 12px; }
.card-actions .btn { flex: 1; padding: 9px 12px; font-size: 0.88rem; }

/* ── Quiz ── */
#quizContainer { max-width: 680px; margin: 0 auto; }
.quiz-score-bar {
  display: flex; justify-content: space-between; align-items: center;
  background: white; border-radius: 14px; padding: 12px 22px;
  margin-bottom: 18px; box-shadow: var(--card-shadow);
}
.quiz-card { background: white; border-radius: 22px; box-shadow: 0 8px 30px rgba(0,0,0,0.1); padding: 36px; text-align: center; }
.quiz-chinese { font-size: 4rem; font-weight: bold; color: var(--dark); margin: 10px 0; }
.quiz-pinyin  { font-size: 1.5rem; color: #e63946; font-family: monospace; margin-bottom: 26px; }
.quiz-lbadge  { display: inline-block; padding: 4px 14px; border-radius: 20px; background: var(--primary); color: white; font-size: 0.85rem; font-weight: 700; margin-bottom: 6px; }

.quiz-options { display: grid; grid-template-columns: 1fr 1fr; gap: 12px; margin-top: 10px; }
.quiz-opt {
  padding: 15px 12px; border: 2px solid #e0e0e0; border-radius: 14px;
  background: white; font-size: 0.95rem; cursor: pointer;
  transition: all 0.18s; font-family: inherit; line-height: 1.3; text-align: center;
}
.quiz-opt:hover:not(:disabled) { border-color: var(--primary); background: #f0f2ff; }
.quiz-opt.correct { background: #d4edda; border-color: var(--success); color: #155724; font-weight: 700; }
.quiz-opt.wrong   { background: #f8d7da; border-color: var(--danger);  color: #721c24; }
.quiz-opt:disabled { cursor: default; }

.quiz-feedback { margin: 16px 0 8px; font-size: 1.1rem; font-weight: 700; min-height: 1.8rem; }
.quiz-feedback.correct { color: #0a5e2a; }
.quiz-feedback.wrong   { color: #8b0000; }

.quiz-sentence { background: #f8f9ff; border-left: 3px solid var(--primary); border-radius: 0 8px 8px 0; padding: 10px 14px; margin: 10px 0; text-align: left; font-size: 0.88rem; display: none; }
.quiz-nav { display: flex; justify-content: center; gap: 12px; margin-top: 22px; }

.quiz-end { text-align: center; background: white; border-radius: 22px; box-shadow: 0 8px 30px rgba(0,0,0,0.1); padding: 50px 36px; }
.quiz-end .score-big { font-size: 5rem; font-weight: bold; color: var(--primary); }
.quiz-end h2 { font-size: 1.8rem; margin: 10px 0; }
.quiz-end p  { color: #555; margin: 8px 0 24px; font-size: 1.05rem; }


.flexBoxIcon { 
  display: flex; 
  margin: 25px auto; 
  justify-content: center; 
  align-items: center; 
  gap: 20px; 
  max-width: 300px; 
}
.flexBoxIcon a {
  transition: transform 0.2s ease;
}
.flexBoxIcon a:hover {
  transform: scale(1.1);
}
.flexBoxIcon img {
  width: 36px;
  height: 36px;
  object-fit: contain;
}

/* ── Empty state ── */
.empty-state { text-align: center; padding: 60px 20px; color: #888; font-size: 1.1rem; grid-column: 1 / -1; }
.empty-state .big-emoji { font-size: 3rem; margin-bottom: 12px; }

/* ── Footer ── */
footer { text-align: center; margin-top: 50px; padding: 22px; color: #777; font-size: 0.88rem; border-top: 1px solid #ddd; }
footer a { color: var(--primary); }

/* ── Responsive ── */
@media (max-width: 768px) {
  body { padding: 10px; }
  h1 { font-size: 2rem; }
  .subtitle { font-size: 1rem; }
  .controls { flex-direction: column; align-items: center; gap: 8px; }
  .word-grid { grid-template-columns: 1fr; gap: 16px; }
  .quiz-options { grid-template-columns: 1fr; }
  .quiz-chinese { font-size: 3rem; }
  .quiz-card { padding: 24px; }
  .flexBoxIcon { 
    gap: 15px; 
    margin: 15px auto; 
    max-width: 250px; 
  }
  .flexBoxIcon img { width: 32px; height: 32px; }
  footer { margin-top: 30px; padding: 16px; }
}

@media (max-width: 480px) {
  h1 { font-size: 1.8rem; }
  .mode-tabs { flex-direction: column; gap: 8px; }
  .tab-btn { padding: 8px 20px; font-size: 0.9rem; }
  .controls { margin: 6px 0; }
  select, input[type="text"] { min-width: 200px; padding: 8px 12px; font-size: 0.9rem; }
  .btn { padding: 8px 16px; font-size: 0.9rem; }
  .stats { padding: 12px 16px; }
  .stats-row { gap: 12px; font-size: 0.9rem; }
  .card { padding: 16px; }
  .chinese { font-size: 2rem; }
  .pinyin { font-size: 1.1rem; }
  .meaning { font-size: 1.1rem; }
  .quiz-score-bar { padding: 10px 16px; }
  .quiz-card { padding: 20px; }
  .quiz-chinese { font-size: 2.5rem; }
  .quiz-pinyin { font-size: 1.3rem; }
  .quiz-opt { padding: 12px 10px; font-size: 0.9rem; }
  .quiz-end { padding: 30px 20px; }
  .quiz-end .score-big { font-size: 4rem; }
  .quiz-end h2 { font-size: 1.5rem; }
  .flexBoxIcon { 
    flex-direction: column; 
    gap: 10px; 
    margin: 10px auto; 
    max-width: 200px; 
  }
  .flexBoxIcon a { display: flex; justify-content: center; }
}

@media (min-width: 769px) and (max-width: 1024px) {
  .word-grid { grid-template-columns: repeat(auto-fill, minmax(320px, 1fr)); gap: 20px; }
  .quiz-options { grid-template-columns: 1fr 1fr; }
  .flexBoxIcon { 
    gap: 25px; 
    max-width: 350px; 
  }
}

/* ── General Mobile Improvements ── */
@media (max-width: 768px) {
  .tab-btn, .btn, .quiz-opt { min-height: 44px; } /* iOS touch target size */
  .audio-btn { width: 40px; height: 40px; }
  .card-actions .btn { min-height: 40px; }
}

/* ── High DPI Displays ── */
@media (-webkit-min-device-pixel-ratio: 2), (min-resolution: 192dpi) {
  .chinese { font-weight: 600; }
  .quiz-chinese { font-weight: 600; }
}

@media (min-width: 1025px) {
  .word-grid { grid-template-columns: repeat(auto-fill, minmax(350px, 1fr)); gap: 24px; }
  .flexBoxIcon { 
    gap: 30px; 
    max-width: 400px; 
  }
}

/* ── Large Screens (TVs, 4K Monitors) ── */
@media (min-width: 1440px) {
  body { max-width: 1400px; }
  h1 { font-size: 3rem; }
  .word-grid { grid-template-columns: repeat(auto-fill, minmax(400px, 1fr)); gap: 28px; }
  .quiz-card { max-width: 800px; margin: 0 auto; }
  .quiz-chinese { font-size: 5rem; }
  .quiz-pinyin { font-size: 1.8rem; }
  .flexBoxIcon { 
    gap: 35px; 
    max-width: 450px; 
  }
}

/* ── Ultra-Wide Screens ── */
@media (min-width: 1920px) {
  body { max-width: 1600px; }
  .word-grid { grid-template-columns: repeat(auto-fill, minmax(450px, 1fr)); gap: 32px; }
  .quiz-card { max-width: 900px; }
  .quiz-options { grid-template-columns: repeat(3, 1fr); }
}

/* ── Orientation-Specific Adjustments ── */
@media (max-width: 768px) and (orientation: landscape) {
  h1 { font-size: 1.5rem; }
  .subtitle { font-size: 0.9rem; }
  .card { padding: 14px; }
  .chinese { font-size: 1.8rem; }
  .pinyin { font-size: 1rem; }
  .quiz-card { padding: 18px; }
  .quiz-chinese { font-size: 2.2rem; }
  .quiz-pinyin { font-size: 1.1rem; }
  .flexBoxIcon { 
    flex-direction: row; 
    justify-content: center; 
    gap: 20px; 
    margin: 10px auto; 
    max-width: 250px; 
  }
  .flexBoxIcon img { width: 28px; height: 28px; }
}

/* ── Touch Device Optimizations ── */
@media (hover: none) and (pointer: coarse) {
  .card:hover { transform: none; box-shadow: var(--card-shadow); }
  .btn:hover { opacity: 1; transform: none; }
  .audio-btn:hover { transform: none; }
  .quiz-opt:hover:not(:disabled) { border-color: #e0e0e0; background: white; }
}