"

From 2014.igem.org

//STICKY NAV $(document).ready(function () {

 var top = $('#nav').offset().top - parseFloat($('#nav').css('marginTop').replace(/auto/, 500));
 $(window).scroll(function (event) {
   // what the y position of the scroll is
   var y = $(this).scrollTop();

   // whether that's below the form
   if (y >= top) {
     // if so, ad the fixed class
     $('#nav').addClass('fixed');
   } else {
     // otherwise remove it
     $('#nav').removeClass('fixed');
   }
 });

});