JSFiddle - React, Tailwind, and code Playground

HTML

<div class="has-flex">
    <div class="flexed first"></div>
</div>

CSS

body {
    padding: 30px 0;
}

.has-flex {
    display: flex;
    width: 300px;
    margin: 0 auto;
    border: 1px solid #333;
    height: 300px;
}
.flexed {
    margin: auto;
    background: lightblue;
    width: 100px;
    height: 100px;
}