Feedbin: Keep selected centered

feedbin-center.js

// ==UserScript==
// @name         Feedbin: Keep selected centered
// @namespace    http://tampermonkey.net/
// @version      0.1
// @description  Keeps the selected item vertically centered in Feedbin
// @author       Ross Wintle
// @match        https://feedbin.com/
// @icon         https://www.google.com/s2/favicons?domain=feedbin.com
// @grant        none
// ==/UserScript==

(function() {
    'use strict';

    document.addEventListener('keyup', function (ev) {
        if (ev.key === 'ArrowDown' || ev.key === 'ArrowUp') {
            let entry = document.querySelector( 'li.entry-summary.selected' );
            let entryPos = entry.offsetTop;
            let scrollTo = entryPos - (document.body.offsetHeight / 2) + (entry.offsetHeight / 2);
            document.querySelector('.entries').scrollTo({
                top: scrollTo,
                left: 0,
                behavior: 'smooth'
            });
        }
    })

})();