JSFiddle - React, Tailwind, and code Playground

HTML

<script src="http://www.polymer-project.org/platform.js?20140312"></script>
<div>LIGHT</div>

CSS

div::shadow .red {
    color:red;
}

JavaScript

var div = document.querySelector('div');
    var root = div.createShadowRoot();
    root.innerHTML = '<div class="red">SHADOW</div>';