simple-s3-gallery/templates/card.html

<div class="col-md-3">
  <a href="{{FULLLINK}}" target="{{FULLLINK}}">
      <div class="card mb-3 bg-dark text-white">
          <div class="card-header">{{TITLE}}</div>
          <img class="card-img" width="250" src="{{THUMBNAIL}}" />
      </div>
  </a>
</div>