JSFiddle - React, Tailwind, and code Playground

HTML

<div id="container">
    <div id="overlay"></div>
    <iframe src="http://www.google.com/" />
</div>

CSS

#container {
    position: relative;
}

#overlay {
    position: absolute;
    z-index: 1;
    height: 500px;
    width: 500px;
    box-shadow: inset 0 0 5px black;
}

iframe {
    height: 500px;
    width: 500px;
    border: 0 none;
}