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HTML 

              
                <div class="container">
  <!-- 画像があるカード1 (2カラムになる) -->
  <div class="card">
    <img src="https://web-saku.net/wp-content/uploads/2025/06/cat-150a.jpg" alt="サンプル画像1">
    <div class="card__body">
      <h2>画像ありカードのタイトル1</h2>
      <p>このカードには画像が含まれているため、画像が左、テキストが右の2カラムレイアウトになります。</p>
    </div>
  </div>

  <!-- 画像がないカード1 (1カラムになる) -->
  <div class="card">
    <div class="card__body">
      <h2>画像なしカードのタイトル1</h2>
      <p>このカードには画像が含まれていないため、シンプルな1カラムレイアウトになります。画像がない分、テキストが全幅を使います。</p>
    </div>
  </div>

  <!-- 画像があるカード2 (2カラムになる) -->
  <div class="card">
    <img src="https://web-saku.net/wp-content/uploads/2025/06/cat-150b.jpg" alt="サンプル画像2">
    <div class="card__body">
      <h2>画像ありカードのタイトル2</h2>
      <p>こちらも画像を含むカードなので、画像とテキストで構成される2カラムレイアウトになります。</p>
    </div>
  </div>

  <!-- 画像がないカード2 (1カラムになる) -->
  <div class="card">
    <div class="card__body">
      <h2>画像なしカードのタイトル2</h2>
      <p>このカードも画像がないため、コンテンツが縦に並ぶ1カラムレイアウトになります。シンプルな情報の表示に適しています。</p>
    </div>
  </div>
</div>
!

CSS 

              
                body {
  font-family: sans-serif;
  background-color: #f4f4f4;
  padding: 20px;
}

.container {
  max-width: 900px;
  margin: 0 auto;
  display: grid; /* カードを縦に並べるためのグリッドコンテナ */
  gap: 20px;
}

/* カードの共通スタイル */
.card {
  border: 1px solid #ddd;
  background-color: #fff;
  border-radius: 8px;
  overflow: hidden; /* 画像がはみ出さないように */
  box-shadow: 0 2px 5px rgba(0,0,0,0.1);
  padding: 15px; /* デフォルトのパディング */
}

.card h2 {
  margin-top: 0;
  color: #333;
}

.card p {
  margin-bottom: 0;
  color: #666;
}

.card img {
  max-width: 100%;
  height: auto;
  display: block; /* 画像の下の余白をなくす */
  border-radius: 4px; /* 角を丸める */
}

/* ★ここが:has()のキモです！★ */

/* .card が <img>要素 を子孫に持っている場合 */
.card:has(img) {
  display: flex; /* Flexboxコンテナにする */
  align-items: flex-start; /* 上揃え */
  gap: 20px; /* 画像とテキストの間の余白 */
  padding: 0; /* Flexbox化するため、親のパディングは一度リセット */
}

/* 画像があるカード内の画像スタイル */
.card:has(img) img {
  flex-shrink: 0; /* 画像は縮まない */
  flex-basis: 150px; /* 画像の固定幅 */
  width: 150px; /* IE/Edgeの古いFlexboxバグ対策 */
  height: 150px; /* 高さを固定 */
  object-fit: cover; /* 画像がはみ出す場合の表示方法 */
  border-radius: 8px 0 0 8px; /* カード全体の角丸と合わせる */
}

/* 画像があるカード内のテキストコンテンツのラッパー */
.card:has(img) .card__body {
  flex-grow: 1; /* 残りのスペースを全て埋める */
  padding: 15px; /* テキストコンテンツのパディング */
}
!

JS
!
999px

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