JSFiddle - React, Tailwind, and code Playground

HTML

<div id="linkel">These are linkel's dimensions in 'em' units, or not.</div>

CSS

#linkel {
height: 20em;
width: 20em;
}

JavaScript

var w = $("#linkel").css('width');
var h = $("#linkel").css('height');
document.write('width= ' + w + ' and  height= ' + h);