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, "2");
    var fontElements = document.getElementsByTagName("font");
    for (var i = 0, len = fontElements.length; i < len; ++i) {
        if (fontElements[i].size == "2") {
            fontElements[i].removeAttribute("size");
            fontElements[i].style.fontSize = "30px";
        }
    }
}