JSFiddle - React, Tailwind, and code Playground

HTML

<div class="one"> 1. Vertically align me </div>
<div class="two"><span> 2. Vertically align me </span></div>

CSS

div {
    border:1px black solid;
    height:400px;
    width:400px;
}

div.one {
    display:table-cell;
    vertical-align:middle;
}

div.two {
    position:relative;
}

div.two span {
    position:absolute;
    top:50%;
}