body {
    font-family: Arial, sans-serif;
    padding: 20px;
    background: #fafafa;
    color: #333;
  }
  
  header {
    text-align: center;
    margin-bottom: 30px;
  }
  
  h1 {
    margin-bottom: 5px;
    font-size: 28px;
  }
  
  .subtitle {
    font-size: 14px;
    color: #666;
  }
  
  h2 {
    margin-top: 30px;
    margin-bottom: 10px;
    font-size: 20px;
  }
  
  .chapter-grid, .mode-grid {
    display: grid;
    grid-template-columns: repeat(3, 1fr);
    gap: 10px;
  }
  
  .chapter-btn, .mode-btn, .start-btn, .next-btn {
    padding: 12px;
    font-size: 16px;
    background: white;
    border: 2px solid #007bff;
    border-radius: 8px;
    color: #007bff;
  }
  
  .chapter-btn.selected {
    background: #007bff;
    color: white;
  }
  
  .start-btn {
    width: 100%;
    margin-top: 20px;
    background: #28a745;
    color: white;
    border-color: #28a745;
  }
  
  .next-btn {
    width: 100%;
    margin-top: 20px;
    background: #007bff;
    color: white;
  }
  
  .hidden {
    display: none;
  }
  
  .option-btn {
    width: 100%;
    padding: 12px;
    margin: 8px 0;
    background: white;
    border: 2px solid #555;
    font-size: 17px;
    border-radius: 6px;
  }
  
  .option-btn:hover {
    background: #efefef;
  }
/* 結果表示 */
.result-area {
    font-size: 20px;
    padding: 10px;
    margin-top: 10px;
    text-align: center;
  }
  
  /* 選択肢の正解ハイライト */
  .choice-btn {
    font-size: 22px;        /* 文字 */
    padding: 16px 20px;     /* ボタンの大きさ */
    margin: 10px 0;
    width: 100%;            /* スマホで押しやすく */
  }  

  .choice-btn.correct {
    background-color: #4caf50 !important;
    color: white;
  }
  
  /* 不正解（押せなくなったボタン） */
  .choice-btn.wrong {
    background-color: #e57373 !important;
    color: white;
    opacity: 0.6;
  }

  #question-box {
    font-size: 28px;   /* ← ここを大きく */
    line-height: 1.6;
    margin-bottom: 20px;
  }

  #example-ja {
    font-size: 20px;
    margin-top: 10px;
    color: #555;
  }
  
  .book-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(160px, 1fr));
    gap: 14px;
  }
  
  .book-btn {
    font-size: 20px;
    padding: 20px 12px;
    border-radius: 10px;
    background: #f4f8ff;
    border: 2px solid #4a7bd0;
    cursor: pointer;
  }
  
  .book-btn:disabled {
    opacity: 0.5;
    cursor: not-allowed;
  }