JSFiddle - React, Tailwind, and code Playground

HTML

<button id="btnChange">Change width</button>
<br>
<div id="mydiv" class="mydiv">test</div>

CSS

.mydiv {
    width:50px;
    background-color:red;
}

JavaScript

var b = document.getElementById("btnChange");
b.onclick = function(event) {
    var d = document.getElementById("mydiv");
    if(d != null) {
        d.style.width = "100px";
    }
};