JSFiddle - React, Tailwind, and code Playground

HTML

<ol>
    <li>a</li>
    <li>a</li>
    <li>a</li>
    <li>a</li>
    <li>a</li>
    <li>a</li>
    <li>a</li>
    <li>a</li>
    <li>a</li>
    <li>a</li>
    <li>a</li>

</ol>

CSS

ol {
    height: 50px;
    border: 1px solid #000;
    overflow: scroll;
}

JavaScript

var ol = document.querySelector('ol');
var olHeight = ol.offsetHeight;

console.log('height:' + olHeight);

ol.addEventListener('scroll', function (event) {
    console.log(ol.scrollTop);    
});