Mobile Responsiveness when Pressing Home Menu

Question

http://www.honorshumanities.umd.edu

The lower navigation menu works on desktop, but on mobile phones, the navigation menu disappears after clicking it. Below is the JavaScript:

(function($) {

    skel.breakpoints({
        xlarge: '(max-width: 1680px)',
        large: '(max-width: 1140px)',
        medium: '(max-width: 980px)',
        small: '(max-width: 736px)',
        xsmall: '(max-width: 480px)',
        xxsmall: '(max-width: 320px)'
    });

    $(function() {

        var $window = $(window),
            $body = $('body');

        // Disable animations/transitions until the page has loaded.
            $body.addClass('is-loading');

            $window.on('load', function() {
                window.setTimeout(function() {
                    $body.removeClass('is-loading');
                }, 250);
            });

        // Fix: Placeholder polyfill.
            $('form').placeholder();

        // Prioritize "important" elements on mobile.
            skel.on('+mobile -mobile', function() {
                $.prioritize(
                    '.important\\28 mobile\\29',
                    skel.breakpoint('mobile').active
                );
            });

        // Scrolly.
            $('.scrolly').scrolly();

    });

})(jQuery);