responsive card header
<div class="card" style="width: 18rem;">
<div class="card-header">
Featured
</div>
<ul class="list-group list-group-flush">
<li class="list-group-item">Cras justo odio</li>
<li class="list-group-item">Dapibus ac facilisis in</li>
<li class="list-group-item">Vestibulum at eros</li>
</ul>
</div>