JSFiddle - React, Tailwind, and code Playground

HTML

<div id="parent">
    THIS IS THE PARENT
    <div id="child">
        THIS IS THE CHILD
    </div>
</div>

CSS

html, body {
    margin: 0;
    padding: 0;
}

#parent {
    background-color: red;
    width: 400px;
    height: 600px;
}

#child {
    background-color: green;
    width: 400px;
    height: 100px;
}

JavaScript

$("#child").css({"position" : "absolute", "top" : $("#child").parent().height() - $("#child").height()});