JSFiddle - React, Tailwind, and code Playground

HTML

<div id="a">
    <div id="b"></div>
</div>

CSS

#a {
  display: block;
  width: 100px;
  height: 100px;
  line-height: 100px;
  float: left;
  border: 1px solid red;
  text-align: center;
}
 
#b {
    display: inline-block;
    background: gray;
    width: 50px;
    height: 50px;
    vertical-align: middle;
}