JSFiddle - React, Tailwind, and code Playground

HTML

<style id="output"></style>
<textarea id="input"></textarea>
<p>Enter something like <pre>body { background: red; }</pre></p>

JavaScript

document.getElementById('input').onkeydown = function() {
    document.getElementById('output').styleSheet.cssText = this.value;
};

document.getElementById('input').onkeyup = function() {
    document.getElementById('output').styleSheet.cssText = this.value;
};