CODE EXAMPLE FOR HTML

collapse card in bootstrap 4

<div class="card">
    <div class="card-header">
        <a data-toggle="collapse" href="#test-block" aria-expanded="true" aria-controls="test-block">
            card header
        </a>
    </div>
    <div id="test-block" class="collapse">
        <div class="card-block">
            card block
        </div>
    </div>
</div>