flex-sm-fill
html bootstrap5 Sample
ナビゲーション:flex
<nav class="nav nav-pills flex-column flex-sm-row">
<a class="flex-sm-fill text-sm-center nav-link active" href="#">アクティブ</a>
<a class="flex-sm-fill text-sm-center nav-link" href="#">リンク</a>
<a class="flex-sm-fill text-sm-center nav-link disabled" href="#">無効</a>
</nav>