JSFiddle - React, Tailwind, and code Playground

HTML

<h3>No Rounded Corners :(</h3>
<div class="rc">
    <video src="http://mirrorblender.top-ix.org/peach/bigbuckbunny_movies/big_buck_bunny_480p_stereo.ogg"  height="240"></video>
</div>
<h3>Rounded Corners :)</h3>
<div class="rc">
    <img src="http://www.lorempixum.com/320/240">
</div>

CSS

.rc{
    width:320px;
    -moz-border-radius:40px;
    border-radius:40px;
    overflow:hidden;
}