Sample Pop Box - Click or Tap Me
video {
border-radius: 6px;
width: 100%;
}
<video controls src="/products/staging/vids/mp/big_buck_bunny_720p_1mb.mp4" type="video/mp4"></video>
Do not set a width. That is all you need to do to make the video responsive. The width goes in the CSS above and is always set to 100%, allowing the container you use to determine video width.