JSFiddle - React, Tailwind, and code Playground

HTML

<div class="flex-container">
    <div class="item">
    </div>
</div>

CSS

html, body {
  height: 100%;
  margin: 0px;
}

.flex-container {
	display: flex;
	align-items: center;
    justify-content: center;
    height: 100%;
}

.item {
    background-color: blue;
    height: 50px; 
    width: 50px;
}