JSFiddle - React, Tailwind, and code Playground

HTML

<div class="centered d1">
    <div class="centered d2">

    </div>
</div>

CSS

body, html {
    width: 100%;
    height: 100%;
}

body {
    position: relative;
    background: green;
}

.centered {
    position: absolute;
    margin: auto;

    display: block;

    bottom: 0px;
    left: 0px;
    top: 0px;
    right: 0px;
}

.d1 {
    background: yellow;
    width: 50px;
    height: 50px;
}

.d2 {
    background: red;
    opacity: 0.7;
    width: 250px;
    height: 250px;
}