JSFiddle - React, Tailwind, and code Playground

HTML

<div class="outer">
    <div class="inner"></div>
</div>

CSS

.outer{
    background: red;
    margin: 0 auto;
    width:100px;
    height:100px;
    position:relative;
}

.inner{
    position:absolute;
    width:20px;
    height:20px;
    background:blue;
    top:0;
    margin: auto;
    left:0;
    right:0px;
    bottom:0;
}