<style>
  .aspect-ratio {
    padding-top: calc(1 / (16 / 9) * 100%);
    position : relative;
  }

  .aspect-wrapper {
    position: absolute;
    top:0;
    left:0;
    width:100%;
    height:100%;
  }
</style>

<div class="aspect-ratio">
  <div class="aspect-wrapper">
    Maintains block aspect ratio at different resolutions
  </div>
</div>