JSFiddle - React, Tailwind, and code Playground

HTML

<div id="d">hey</div>

CSS

div {
    width: 100px;
    height: 100px;
    -my-foo: 42px;
}

JavaScript

console.log(window.getComputedStyle(document.getElementById("d"), null));
console.log(document.styleSheets[2].cssRules[1]);