ライン型アコーディオン（シンプル＆スタイリッシュ）

<div class="accordion-line">
  <div class="accordion-item">
    <button class="accordion-question">Q. このデザインの特徴は？</button>
    <div class="accordion-answer">
      <p>A. 下線を使ったミニマルな構成で、ページに馴染みやすいです。</p>
    </div>
  </div>

  <div class="accordion-item">
    <button class="accordion-question">Q. 複数開けますか？</button>
    <div class="accordion-answer">
      <p>A. はい、複数同時に開くことができます。</p>
    </div>
  </div>
</div>

.accordion-line {
  max-width: 600px;
  margin: 50px auto;
  font-family: sans-serif;
}

.accordion-item {
  border-bottom: 1px solid #ccc;
  margin-bottom: 12px;
}

.accordion-question {
  background: none;
  border: none;
  width: 100%;
  text-align: left;
  padding: 16px 0;
  font-size: 16px;
  font-weight: 500;
  color: #333;
  cursor: pointer;
  position: relative;
  transition: color 0.2s ease;
}

.accordion-question::after {
  content: '+';
  position: absolute;
  right: 0;
  top: 50%;
  transform: translateY(-50%);
  font-weight: bold;
  transition: transform 0.3s ease;
}

.accordion-question.active::after {
  content: '−';
}

.accordion-answer {
  display: none;
  padding: 8px 0 16px;
  font-size: 14px;
  color: #555;
  line-height: 1.6;
}

document.querySelectorAll('.accordion-question').forEach(btn => {
  btn.addEventListener('click', () => {
    const answer = btn.nextElementSibling;
    btn.classList.toggle('active');
    answer.style.display = answer.style.display === 'block' ? 'none' : 'block';
  });
});