jQuery code not working

Hi, I’m trying to manually implement a sidebar element that becomes fixed after some scrolling. In order to do it, I’m using few lines of jQuery that after scroll add a class with position:fixed property to the element, and on a testing environment it works fine.
However when implementing it on wordpress, it doesn’t seem to work. I put the following script in the custom javascript section of my theme admin panel, it seems to be loaded on the frontend but nothing happens.

$(window).scroll(function(){
      if ($(this).scrollTop() > 235) {
          $('#sidebar-2').addClass('fix-it');
      } else {
          $('#sidebar-2').removeClass('fix-it');
      }
});

Here’s also some dummy code to explain what I’m trying to accomplish: fiddle

Am I missing something? Thanks for your help.