JSFiddle - React, Tailwind, and code Playground

HTML

<body>
    <div id='_1'>
    </div>
</body>

CSS

#_1 {
    display: block;
    width: 50px;
    height: 50px;
    left: 50px;
    top: 20px;
    background-color: red;
    border: 1px solid red;
    position: absolute;
}

JavaScript

$(document).ready(function() {
   var l = window.getComputedStyle(document.getElementById('_1'),"").left;
   l = parseFloat(l);
    alert(l);
});