align-self-stretch

bootstrap5.css

.align-self-stretch {
  -ms-flex-item-align: stretch !important;
  align-self: stretch !important;
}

html bootstrap5 Sample

flexコンテナー内のアイテムの配置/自身ストレッチ：align-self-stretch

flex文字01

flex文字02（align-self-stretch）

flex文字03

  <div class="d-flex" style="height: 100px">
    <div>flex文字01</div>
    <div class="align-self-stretch">flex文字02（align-self-stretch）</div>
    <div>flex文字03</div>
  </div>