https://www.panika.kz/wp-content/themes/panika/zvonok/js/popup.js

1var popupHeight, windowHeight, scrollTop;
2
3$(document).ready(function(){
4    
5    $('.popup_button').click(function(e){
6        e.preventDefault();
7        var popup = $(this).attr('rel');
8        showPopup(popup);
9    });
10	
11    $('.popup_bg, .popup_close').click(function(e){
12        e.preventDefault();
13        $('.popup_bg').fadeOut();
14        $('.popup_window').fadeOut();
15    });
16	
17    
18});
19
20$(window).scroll(function(){
21    windowHeight = $(window).height();
22    scrollTop = $(window).scrollTop();
23});
24
25function showPopup(popup){
26    $('.popup_bg').fadeIn();
27    $('#'+ popup).fadeIn();
28    popupHeight = $('#'+ popup).outerHeight();
29    windowHeight = $(window).height();
30    scrollTop = $(window).scrollTop();
31		
32    if(windowHeight < popupHeight){
33        $('#'+ popup).css('top',scrollTop);
34    }else{
35        $('#'+ popup).css('top',(windowHeight - popupHeight) / 2 + scrollTop);
36    }
37}