Magnific PopUP Fixed Header (fix)

gistfile1.txt

/**
* Author - https://github.com/dimsemenov/Magnific-Popup/issues/350#issuecomment-33362275
*/

$('#gallery').magnificPopup({
    delegate: 'a',
    type: 'image',
    gallery: {
        enabled:true
    },
    callbacks: {
        open: function() {
            $nav.css({'overflow-y': 'scroll'});
        },
        close: function() {
            $nav.css({'overflow-y': 'visible'});
        }
    }
});