cards.template.html

<!-- cards.template.html -->
<div class="cards">
  <template is="dom-repeat" items="[[cards]]">
    <div class$="[[getClass(item)]]" on-tap="flip">
        <div class="face cover">
          <img src="{{item.coverImageUrl}}" alt="cover">
        </div>
        <div class="face value">
          <img src="{{item.imageUrl}}" alt="card">
        </div>
    </div>
  </div>
</div>
<style>
  // css here
</style>