JSFiddle - React, Tailwind, and code Playground

HTML

<div id='parent'>
    <div id='centered-child'></div>
</div>

CSS

#parent {
    display: block;
    background-color: blue;
    width: 250px;
    height: 250px;
    position: relative;
}
#centered-child {
    position: absolute;
    left: 0;
    right: 0;
    top: 0;
    bottom: 0;
    margin: auto auto;
    background-color: red;
    width: 100px;
    height: 100px;
}