JSFiddle - React, Tailwind, and code Playground

HTML

<div class="contenedor">
    <div class="elementoACentrar">
        &nbsp;
    </div>
</div>

CSS

.contenedor {
  position: relative;
  height:500px;
  width:500px;  
  background-color:#000;
}
.elementoACentrar {
  position: absolute;
  top: 50%;
  transform: translateY(-50%);
  width:200px;
  height:200px;
  background-color:#666;
  margin-left: 150px ;
}