https://www.smallingerland.nl/js/custom/accordion.js

1(function ($) {
2    $(document).ready(function () {
3        $('#accordion_container > ul > li > h3 > button').attr('aria-expanded',"false");
4        $('#accordion_container > ul > li > .accordion-content ').attr('hidden', "hidden");
5        $('#accordion_container > ul > li > h3 ').first().addClass('accordion-toggle-active');
6        $('#accordion_container > ul > li > .accordion-content ').first().addClass('open');
7        $('#accordion_container > ul > li > .accordion-content ').first().removeAttr('hidden');
8        $('#accordion_container > ul > li > h3 > button').first().addClass('accordion-toggle-active').attr('aria-expanded',"true");
9
10        $('#accordion_container > ul > li > h3 > button').click(function () {
11            $('#accordion_container h3').removeClass('accordion-toggle-active');
12            $('#accordion_container button').removeClass('accordion-toggle-active').attr('aria-expanded',"false");
13            $('#accordion_container > ul > li > .accordion-content ').removeClass('open');
14            $('#accordion_container > ul > li > .accordion-content ').attr('hidden', "hidden");
15
16            $(this).parent().addClass('accordion-toggle-active');
17            $(this).addClass('accordion-toggle-active').attr('aria-expanded',"true");
18            $(this).parent().next().addClass('open');
19            $(this).parent().next().removeAttr('hidden');
20        });
21    });
22})(jQuery);