bootstrap4

bootstrap4.css

.card-img-bottom {
  width: 100%;
  border-bottom-right-radius: calc(0.25rem - 1px);
  border-bottom-left-radius: calc(0.25rem - 1px);
}

bootstrap4.css

@media (min-width: 576px) {
  .card-group {
    -ms-flex-flow: row wrap;
    flex-flow: row wrap;
  }
  .card-group > .card {
    -ms-flex: 1 0 0%;
    flex: 1 0 0%;
    margin-bottom: 0;
  }
  .card-group > .card + .card {
    margin-left: 0;
    border-left: 0;
  }
  .card-group > .card:not(:last-child) {
    border-top-right-radius: 0;
    border-bottom-right-radius: 0;
  }
  .card-group > .card:not(:last-child) .card-img-top,
  .card-group > .card:not(:last-child) .card-header {
    border-top-right-radius: 0;
  }
  .card-group > .card:not(:last-child) .card-img-bottom,
  .card-group > .card:not(:last-child) .card-footer {
    border-bottom-right-radius: 0;
  }
  .card-group > .card:not(:first-child) {
    border-top-left-radius: 0;
    border-bottom-left-radius: 0;
  }
  .card-group >

■カード：card：コンポーネント：カードに画像を配置する　card-img-top　card-img-bottom

カードの内容

    <!-- カード上部に画像を配置：card-img-top -->
    <div class="card mb-3" style="max-width: 25rem;">
    <img class="card-img-top" src="https://via.placeholder.com/318x180/FFFF00/000000?text=.card-img-top" alt="...">
    <div class="card-body">
      <p class="card-text">カードの内容</p>
    </div>
  </div>
    <!-- カード下部に画像を配置：card-img-bottom -->
    <div class="card" style="max-width: 25rem;">
    <div class="card-body">
      <p class="card-text">カードの内容</p>
    </div>
    <img class="card-img-bottom" src="https://via.placeholder.com/318x180/FFFF00/000000?text=.card-img-bottom" alt="..."> </div>
</div>