JSFiddle - React, Tailwind, and code Playground

HTML

<div id="testbox">
    <div class="testbox2">
    </div>
</div>

CSS

#testbox{
  border: 3px solid red;
  width: 200px;
  height: 200px;
  margin: 50px auto 0;
}

.testbox2{
  border: 3px solid blue;
  width:100px;
  height:100px;
  margin: 48px auto;
}