アコーディオン：シンプル｜Accordion: Simple

<div class="container">
  <div class="btn-box">
      <button data-default-text="シンプルアコーディオン" data-open-text="閉じる">シンプルアコーディオン</button>
  </div>
  <div class="more">
      <ul>
          <li>シンプルで使いやすいデザイン</li>
          <li>基本的な開閉アニメーション</li>
          <li>レスポンシブ対応</li>
          <li>軽量で高速</li>
          <li>カスタマイズしやすい</li>
      </ul>
  </div>
</div>

@keyframes fadeIn {
  0% {
    opacity: 0;
    transform: translateY(-10px);
  }
  100% {
    opacity: 1;
    transform: none;
  }
}

.container {
  margin-bottom: 30px;
}

.container .btn-box button {
  width: 100%;
  padding: 20px 25px;
  background: #fff;
  border: 2px solid #ddd;
  border-radius: 8px;
  font-size: 16px;
  font-weight: 600;
  color: #333;
  cursor: pointer;
  transition: all 0.3s ease;
  text-align: left;
}

.container .btn-box button:hover {
  background: #f8f9fa;
  border-color: #adb5bd;
}

.container .more {
  max-height: 0;
  overflow: hidden;
  transition: max-height 0.3s ease;
  background: #fff;
  border: 2px solid #ddd;
  border-top: none;
  border-radius: 0 0 8px 8px;
}

.container .more.appear {
  max-height: 300px;
  animation: fadeIn 0.3s ease;
}

.container .more ul {
  list-style: none;
  padding: 20px;
  margin: 0;
}

.container .more li {
  padding: 12px 0;
  color: #666;
  border-bottom: 1px solid #eee;
}

.container .more li:last-child {
  border-bottom: none;
}

/* レスポンシブ対応 */
@media (max-width: 768px) {
  .container .btn-box button {
    font-size: 14px;
    padding: 15px 20px;
  }
  
  .container .more ul {
    padding: 15px;
  }
}

document.addEventListener('DOMContentLoaded', function() {
    const button = document.querySelector('.btn-box button');
    const content = document.querySelector('.more');
    
    button.addEventListener('click', function() {
        content.classList.toggle('appear');
        
        // ボタンテキストの切り替え
        if (content.classList.contains('appear')) {
            this.textContent = this.dataset.openText || '閉じる';
        } else {
            this.textContent = this.dataset.defaultText;
        }
    });
});