アコーディオン：ミニマリスト｜Accordion: Minimalist

<div class="container">
  <div class="btn-box">
      <button data-default-text="Minimalist Accordion" data-open-text="Close">Minimalist Accordion</button>
  </div>
  <div class="more">
      <ul>
          <li>Clean and minimal design</li>
          <li>Subtle animations</li>
          <li>Focus on typography</li>
          <li>Elegant transitions</li>
          <li>Professional appearance</li>
      </ul>
  </div>
</div>

body {
    font-family: 'Inter', -apple-system, BlinkMacSystemFont, 'Segoe UI', Tahoma, Geneva, Verdana, sans-serif;
    background: #ffffff;
    padding: 20px;
    min-height: 100vh;
    color: #333;
}

.container {
    margin-bottom: 30px;
    max-width: 600px;
    margin-left: auto;
    margin-right: auto;
    position: relative;
}

@keyframes minimalFadeIn {
  0% {
    opacity: 0;
    transform: translateY(-5px);
  }
  100% {
    opacity: 1;
    transform: none;
  }
}

@keyframes underlineExpand {
  0% {
    width: 0;
  }
  100% {
    width: 100%;
  }
}

.container .btn-box button {
  width: 100%;
  padding: 20px 0;
  background: transparent;
  border: none;
  border-bottom: 1px solid #e0e0e0;
  font-size: 18px;
  font-weight: 400;
  color: #333;
  cursor: pointer;
  transition: all 0.3s ease;
  text-align: left;
  position: relative;
  font-family: 'Inter', -apple-system, BlinkMacSystemFont, sans-serif;
  letter-spacing: -0.02em;
}

.container .btn-box button::before {
  content: '';
  position: absolute;
  bottom: -1px;
  left: 0;
  height: 2px;
  background: #333;
  transition: width 0.3s ease;
  width: 0;
}

.container .btn-box button::after {
  content: '+';
  position: absolute;
  right: 0;
  top: 50%;
  transform: translateY(-50%);
  font-size: 24px;
  font-weight: 300;
  color: #666;
  transition: all 0.3s ease;
}

.container .btn-box button:hover {
  color: #000;
}

.container .btn-box button:hover::before {
  width: 100%;
}

.container .btn-box button:hover::after {
  color: #000;
}

.container .more {
  max-height: 0;
  overflow: hidden;
  transition: max-height 0.4s cubic-bezier(0.4, 0, 0.2, 1);
  background: transparent;
}

.container .more.appear {
  max-height: 400px;
  animation: minimalFadeIn 0.3s ease;
}

.container:has(.more.appear) .btn-box button::after {
  transform: translateY(-50%) rotate(45deg);
  color: #000;
}

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

.container .more li {
  padding: 12px 0;
  color: #666;
  font-size: 15px;
  line-height: 1.6;
  border-bottom: 1px solid #f5f5f5;
  font-weight: 300;
  transition: all 0.2s ease;
}

.container .more li:hover {
  color: #333;
  padding-left: 5px;
}

.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: 16px;
    padding: 15px 0;
  }
  
  .container .more ul {
    padding: 15px 0;
  }
  
  .container .more.appear {
    max-height: 300px;
  }
  
  .container .more li {
    font-size: 14px;
    padding: 10px 0;
  }
}

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 || 'Close';
        } else {
            this.textContent = this.dataset.defaultText;
        }
    });
});