<div class="video">
  <div class="yt">
      <iframe width="560" height="315" src="https://www.youtube.com/embed/eIOAtcuK8bU" title="YouTube video player" frameborder="0" allow="accelerometer; autoplay; clipboard-write; encrypted-media; gyroscope; picture-in-picture; web-share" allowfullscreen></iframe>
  </div>
</div>
body{
  background:#333;
}
.video{
  max-width:640px;
}
.yt{
   position: relative;
   width: 100%;
   padding-bottom: 56.25%;
}
.yt iframe {
    position: absolute;
    width: 100%;
    height:100%;
    top: 0;
    left: 0;
}

External CSS

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External JavaScript

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