JSFiddle - React, Tailwind, and code Playground

HTML

<div class="box"></div>

CSS

html {
    height: 100%;
}
body {
    text-align: center;
    height: 100%;
    padding: 0;
    margin: 0;
}
body::before {
    content: "";
    height: 100%;
    display: inline-block;
    vertical-align: middle;
    width: 0;
}
.box {
    width:100px;
    min-height:100px;
    border:solid 1px red;
    margin: 0 auto;
    display: inline-block;
    vertical-align: middle;
}