https://www.tygodnikpowszechny.pl/themes/tygodnik/js/menu_main.js?tm88s4

1//Function to hide ans show top menu depending on scrolling
2var prevScrollPos = Math.max(0, window.pageYOffset);
3window.onscroll = function() {
4  if (document.querySelector('.topbar_mob') === null) {
5    return;
6  }
7  var currentScrollPos = Math.max(0, window.pageYOffset);
8  if (currentScrollPos <= 5 || prevScrollPos > currentScrollPos) {
9    document.querySelector('.topbar_mob').style.top = '0rem';
10    var mobileMenuIcon = document.querySelector('.topbar_mob .menu-icon');
11    if (mobileMenuIcon) {
12      mobileMenuIcon.style.boxShadow = 'none';
13    }
14  } else {
15    document.querySelector('.topbar_mob').style.top = '-150px';
16    // document.querySelector('.topbar_mob .menu-icon').style.boxShadow = '-1px 0 3px 1px rgba(0, 0, 0, 0.3333)';
17  }
18  prevScrollPos = currentScrollPos;
19}
20
21document.addEventListener('DOMContentLoaded', function () {
22  var menuToggle = document.getElementById('menu-toggle');
23  if (!menuToggle) {
24    return;
25  }
26});