JSFiddle - React, Tailwind, and code Playground

HTML

<div id="a">
    <div id="b"></div>    
</div>

CSS

div#a
{
    width: 300px;
    height: 300px;
    border-width:1px;
    border-style: solid;
    
    /* important stuff below */
    display: inline-block; 
}

div#b
{
    width: 60px;
    height: 60px;
    background-color: red;
    
    /* important stuff below */
    position: relative;
    margin: -30px auto 0 auto;
    top: 50%;    
}