<section>
  <div class="vid">
    <iframe width="1280" height="720" src="//www.youtube.com/embed/ByOPXIHaVfQ" frameborder="0" allowfullscreen></iframe>
  </div>
</section>
@import "nib"

section
  width: 70%

.vid
  margin: 2rem
  border: 30px solid red

iframe
  width: 100%
  height: calc((70vw - 60px) * (9/16))
  display: block
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External CSS

This Pen doesn't use any external CSS resources.

External JavaScript

  1. https://cdnjs.cloudflare.com/ajax/libs/jquery/2.1.3/jquery.min.js