How do I center an image in a Bootstrap 4 card? It's a vertical image and it looks wrong being left-aligned. I've been reading the Bootstrap Card documentation and can't find anything about centering the image.
<div class="card-deck">
<div class="card col-sm-3">
<div>
<img class="card-img-top" src="image_URL" alt="alt-text" >
<div class="card-block">
<div class="card-text">
text
</div>
</div>
</div>
</div>
