JSFiddle - React, Tailwind, and code Playground

HTML

<div class="outside">
         <div class="inside">
         </div>
    </div>

CSS

/*CSS#1 does not work*/
.outside{
    background: blue;
    width: 400px;
    height: 400px;
    position: relative;
}
.inside{
    background: red;
    width: 200px;
    height: 200px;
    position: absolute;
    top: 50%;
    margin-top: -100px; /*half height of this div*/
    left: 50%;
    margin-left: -100px;
}