JSFiddle - React, Tailwind, and code Playground

HTML

<body>
    <div class="thing1"></div>
</body>

CSS

body {
    background: #000;
}

.thing1 {
    width: 250px;
    height: 200px;
    margin: 50px;
    background: #fff;
}

.thing2 {    
    margin-left: auto;
    margin-right: auto;
    width: 250px;
    height: 100px;    
    background: #f00;
}