JSFiddle - React, Tailwind, and code Playground

HTML

<div class="windowMiddle"></div>

CSS

.windowMiddle{
    height: 200px;
    width: 300px;
    background: #ccc;
    position: fixed;
    top: 0;
    left: 0;
    right: 0;
    bottom: 0;
    margin: auto;
}