JSFiddle - React, Tailwind, and code Playground

HTML

<body>
    Hello world
</body>

CSS

.redbody {
    background-color: #FF0000;
}

.bluebody {
    background-color: #0000FF;
}

JavaScript

document.body.className='redbody';
console.log(window.getMatchedCSSRules(document.body));
document.body.className='bluebody';
console.log("Class changed");
console.log(window.getMatchedCSSRules(document.body));