<div id="accordion">
<div class="card border-0 mb-4">
<div class="card-header bg-gray border p-0">
<a class="card-link h5 d-block tex-dark mb-0 py-10 px-4" data-toggle="collapse"
href="#collapseOne">
<i class="ti-minus text-primary mr-2"></i> Accordion
</a>
</div>
<div id="collapseOne" class="collapse"
data-parent="#accordion">
<div class="card-body font-secondary text-color pl-0 pb-0">
Lorem ipsum dolor sit amet.
</div>
</div>
</div>
</div>
.card-header used for some extra styling.
Icon is styled on data-toggle="collapse" attribute. So you dont have to use another classes.