If you are using Bootstrap 4.3 you don’t have to wrap card with <a> tag, but instead put it inside card-body, and use stretched-link class. This is much cleaner way.
Visit https://getbootstrap.com/docs/4.3/utilities/stretched-link/ for more details.
If you can’t use Bootstrap 4.3 this is styling for stretched-link class:
.stretched-link::after {
position: absolute;
top: 0;
right: 0;
bottom: 0;
left: 0;
z-index: 1;
pointer-events: auto;
content: "";
background-color: rgba(0,0,0,0);
}
Here is the example:
<link rel="stylesheet" href="https://maxcdn.bootstrapcdn.com/bootstrap/4.3.1/css/bootstrap.min.css">
<div class="card" style="width: 15rem; display: inline-block">
<img class="card-img-top" src="https://placeholdit.imgix.net/~text?txtsize=33&txt=318%C3%97180&w=318&h=180" alt="Card image cap">
<div class="card-body">
<h5 class="card-title">Normal card</h5>
<p class="card-text">Some quick example text to build on the card title and make up the bulk of the card's content.</p>
</div>
</div>
<div class="card" style="width: 15rem; display: inline-block">
<img class="card-img-top" src="https://placeholdit.imgix.net/~text?txtsize=33&txt=318%C3%97180&w=318&h=180" alt="Card image cap">
<div class="card-body">
<h5 class="card-title">Alternative</h5>
<p class="card-text">Some quick example text to build on the card title and make up the bulk of the card's content.</p>
<a href="#" class="stretched-link"></a>
</div>
</div>