JSFiddle - React, Tailwind, and code Playground

HTML

<div class="main">
    <div class="sub"></div>
</div>

CSS

div {
    border: 1px solid black;
}

.main {
    position: relative;
    height: 400px;
}

.sub {
    position: absolute;
    bottom: 0;
    left: 0;
    right: 0;
    height: 200px;
    width: 200px;
    margin: 0 auto;
}