JSFiddle - React, Tailwind, and code Playground

HTML

<div id="Div1"></div>

CSS

#Div1 {
    width: 50px;
    height: 50px;
    border: 1px solid red;
    -webkit-transition: width 1s ease-in;
}
#Div1.expand {
    width: 100px;
}

JavaScript

var element = document.getElementById("Div1");
element.setAttribute("class", "expand");