JSFiddle - React, Tailwind, and code Playground

HTML

<div id="a-middle"></div>

CSS

#a-middle {
    border: 1px solid;
    width: 200px;
    height: 200px;
    margin: 0 auto;
}

JavaScript

var verticalCentering = function () {
    var el = document.querySelector('#a-middle');
    el.style.marginTop = (window.innerHeight - el.offsetHeight) / 2 + 'px';
}
window.addEventListener('resize', verticalCentering);
verticalCentering();