JSFiddle - React, Tailwind, and code Playground

HTML

<div id="backgroundPositionPair"></div>

CSS

#backgroundPositionPair { background-position: 10px 20px; }

JavaScript

var ob = document.getElementById("backgroundPositionPair");
var list = document.defaultView.getComputedStyle(ob, null).getPropertyCSSValue("background-position");
console.log(list.__proto__ === CSSValueList.prototype);
console.log(list.item(0));
try {
    console.log(list.item());
} catch (e) {
    console.log(e);
}