JSFiddle - React, Tailwind, and code Playground

HTML

<div id="first">
      <div id="second"></div>
     </div>

CSS

#first {
        width: 100px;
        height: 100px;
        background: red;
    position: relative;
       }
       #first #second{
           width: 50%;
           height: 50%;
        position: absolute; margin: auto;
           background: green;
    top :0; left: 0; right: 0; bottom: 0;
        }