JSFiddle - React, Tailwind, and code Playground

HTML

<div id="container">
<div id="blackBox">

</div>
</div>

CSS

#container{
  height:600px;
  position:relative;
}
#blackBox{
  height:50px;
  width:50px;
  background-color:black;
  position: absolute;
  top: 50%;
  transform: translateY(-50%);
  -ms-transform: translateY(-50%); /* IE 9 */
  -webkit-transform: translateY(-50%); /* Chrome, Safari, Opera */
}