JSFiddle - React, Tailwind, and code Playground

HTML

<h1>Non Shadow:</h1>
<div><span>Blue.</span></div>
<h1>Shadow:</h1>
<div id="host">Should be blue, but isn't.</div>

CSS

div span {
  color: blue;
}

JavaScript

var shadow = new WebKitShadowRoot(host);
shadow.applyAuthorStyles = true;
shadow.innerHTML = "<span><shadow></shadow></span>";