JSFiddle - React, Tailwind, and code Playground

HTML

<div id="parent">
    Parent
    <div>1</div>
    <div id="child">2</div>
    <div>3</div>
</div>

CSS

div {
    background: #eee;
}
div div {
    width: 100px;
    height: 100px;
    background: #aaa;
    margin: 8px;
}

JavaScript

alert(document.getElementById('child').getBoundingClientRect().top-document.getElementById('parent').getBoundingClientRect().top);