JSFiddle - React, Tailwind, and code Playground

HTML

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

CSS

.base,
.main {
    position: relative;
    top: 25px;
}

.base {
    background-color: blue;
    width: 100px;
    height: 100px;
}

.main {
    background-color: red;
    width: 50px;
    height: 50px;
}

JavaScript

var element = document.querySelector('.main')
console.log(element.offsetTop) //25
console.log(element.getBoundingClientRect().top) //58
console.log(element.getBoundingClientRect().top - element.offsetParent.getBoundingClientRect().top) //25