JSFiddle - React, Tailwind, and code Playground

HTML

<div id="boss">
 <div id="kids"> 
 </div>
</div>

CSS

#boss {
  border: 1px solid #000;
  width: 300px;
  height: 300px;
    display: flex;
  align-items: center;
}

#kids {

  margin: 0 auto;
  border: 1px solid #000;
  width: 150px;
  height: 150px;
}