JSFiddle - React, Tailwind, and code Playground

HTML

<div class="parent">
    <div class="wrapper">
        <div class="sibling">
        </div>
    </div>
</div>

CSS

.parent{
    width: 800px;
    height:400px;
    background-color:red;
    position: relative;
}
.sibling{
    width:300px;
    height:50px;
    background-color: green;
    margin: 0 auto;
}
.wrapper{
    width: 100%;
    position: absolute;
    bottom: 0;
}