JSFiddle - React, Tailwind, and code Playground

HTML

<input type="button" onclick="changeFont()" value="Change font">
<div contenteditable="true">Hello, this is some editable text</div>

JavaScript

function changeFont() {
    document.execCommand("fontSize", false, "7");
    var fontElements = window.getSelection().anchorNode.parentNode
    fontElements.removeAttribute("size");
    fontElements.style.fontSize = "30px";
}