JSFiddle - React, Tailwind, and code Playground

HTML

<div class="a">cool</div>
<div class="b"><iframe width="560" height="315" src="//www.youtube.com/embed/xrMOBKHqqc8?rel=0&autoplay=1" frameborder="0" allowfullscreen></iframe>

CSS

.a { border: solid blue; height: 20px; }

.b {display: none; border: solid green; }

.a:hover + .b { display: block; }

.b:hover { display: block; }