<figure class="vid">
  <iframe width="1280" height="720" src="//www.youtube.com/embed/_xG68lkrMDU?list=UUJr72fY4cTaNZv7WPbvjaSw" frameborder="0" allowfullscreen></iframe>
</figure>
.vid
  margin: 2rem
  border: 30px solid red
  height: (100 * (9/16))vw

iframe
  width: 100%
  height: (100 * (9/16))vw
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