JSFiddle - React, Tailwind, and code Playground

HTML

<body>
<div class="box">

</div>
</body>

CSS

body
{
	background-color:DarkGray;
	display:table;
}

.box
{
    display:table-cell
    margin:0, auto;    
        
	background-color:black;
	
    width:20px;
    height:20px;
}