JSFiddle - React, Tailwind, and code Playground

HTML

<div id='box'></div>

CSS

#box {
   position: fixed;
   background-color: red;
   width: 200px;
height: 200px    
}

JavaScript

var $box = $('#box');

var bw = $box.width() / 2;
var bh = $box.height() / 2;

var wh = $(window).height() / 2;
var ww = $(window).width() / 2;

$box.css({'left': ww-bw, "top": wh-bh})