title: Jquery add CSS class after 'X' amount of viewport height scrolled
body: <p>So I have this jQuery function that adds / removes a CSS class to an element after 600px of the viewport height has been scrolled.</p>
  
  <pre><code>$(window).scroll(function() {    
      var scroll = $(window).scrollTop();    
      if (scroll &gt;= 600) {
          $(".cta_box").addClass('fadeout');
      } else {
          $(".cta_box").removeClass('fadeout');
      }
  });
  </code></pre>
  
  <p>I'd like to tweak it so instead of working based off a pixel value, it works off of the view height css measurement "VH", but the equivalent results are what matter in this case.</p>