JSFiddle - React, Tailwind, and code Playground

HTML

<div id="test1" class="test" contenteditable="true" onkeyup="transferHTML('test1', 'test2');" ></div>
<textarea id="test2"></textarea>

CSS

.test {width:400px;height:200px;background-color:gray;color:black;}
textarea {width:400px;height:200px;background-color:white;color:black;}

JavaScript

function transferHTML(from, to) {
    document.getElementById(to).value =  document.getElementById(from).innerHTML;
}