jQuery qTip not changing classes ?

Hii i am using qTip 2 i want the class ui-tooltip-dark ui-tooltip-shadow but it doesnt shows that class. I have this code:

    $('.selector').qtip({
   content: {
      text: function(api) {
         // R开发者_Go百科etrieve content from custom attribute of the $('.selector') elements.
         return $(this).attr('qtip-content');
        }
      },
      title: {
         text: function(api) {
            // Retrieve content from ALT attribute of the $('.selector') element
            return $(this).attr('alt');
         }
      },
     style: {
      classes: 'ui-tooltip-dark ui-tooltip-shadow';
      }
});

But when i put the code that is on their site it works

Can u please tell me where am i going wrong ?

EDIT

    <script type="text/javascript" class="example">
$(document).ready(function()
{
    $('.selector').qtip({
   content: {
      text: function(api) {
         // Retrieve content from custom attribute of the $('.selector') elements.
         return $(this).attr('qtip-content');
      }
     },
      title: {
         text: function(api) {
            // Retrieve content from ALT attribute of the $('.selector') element
            return $(this).attr('alt');
         }
      },
     style: {
      classes: 'ui-tooltip-dark ui-tooltip-shadow';
      }
});
});
</script>

It might just be a typo in what you've posted but you're missing a curly brace around the content section -

$('.selector').qtip({
   content: {
      text: function(api) {
         // Retrieve content from custom attribute of the $('.selector') elements.
         return $(this).attr('qtip-content');
      }
     },
      title: {
         text: function(api) {
            // Retrieve content from ALT attribute of the $('.selector') element
            return $(this).attr('alt');
         }
      },
     style: {
      classes: 'ui-tooltip-dark ui-tooltip-shadow';
      }
});

EDIT

Try this -

$(document).ready(function()
{
    $('.selector').qtip({
   content: {
      text: function(api) {
         // Retrieve content from custom attribute of the $('.selector') elements.
         return $(this).attr('qtip-content');
      },
      title: {
         text: function(api) {
            // Retrieve content from ALT attribute of the $('.selector') element
            return $(this).attr('alt');
         }
      }
   },
   style: {
      classes: 'ui-tooltip-dark ui-tooltip-shadow'
      }      
    });
});

You should be able to see it working here - http://jsfiddle.net/KaJ9q/