According to the migration docs, the Bootstrap 4 utility classes should be used instead:
<div class="pb-2 mt-4 mb-2 border-bottom">
Page header
</div>
https://codeply.com/go/20jBKvMkHx
- pb-2 – padding bottom 2 spacer units
- mt-4 – margin top 4 spacer units
- mb-2 – margin bottom 2 spacer units
- border-bottom – border-bottom: 1px solid rgb(222, 226, 230)