add and remove an overlay

add and remove an overlay

I am building a new website which has some boxes that changes from classes(done with jquery magic :P).

I want to add an overlay(like the lightbox fading background) to the page when the user clicks on the switch button.

I have tried a couple of things but it seems not to work:
If tried to append a div to the body but that doesn't seems to work:

anybody a idea?


         $(".nl").click(function(){
            $("div.lang_english").fadeOut("fast", function() {
               $(this).fadeIn("fast").removeClass("lang_english").addClass("lang_dutch");

            });
         });