JSFiddle - React, Tailwind, and code Playground

HTML

<div class="content">
            <header>
                <h1 class="maintitle">TEST HTML/CSS CODE</h1>
            </header>
            <h1>Input:</h1>
            <textarea id="textinput" rows=10 cols=50>
            </textarea>
            <h1>Output:</h1>
            <output id="change">
            </output>
            <footer>
            </footer>
        </div>

JavaScript

document.onkeyup = function(){update()};
function update(){
    var c1 = document.getElementById('textinput').value;
    var d1 = document.getElementById('change');
    d1.innerHTML = c1;
}