JSFiddle - React, Tailwind, and code Playground

HTML

<div>
foo
<div id=host></div>
</div>

CSS

div {
  border: 2px solid green;
  margin: 5px;
  padding: 2px;
}

JavaScript

const host = document.getElementById('host');
const shadowRoot = host.attachShadow({mode:'open'});
shadowRoot.innerHTML = '<div>bar</div>'
document.designMode = 'on';