.position().left / Div issue

.position().left / Div issue

Ok so I am new to Jquery and have just started reading through Sitepoint's Jquery: Novice to Ninja book. At this point I am trying to script a navigation bar that has a div highlight the background of each link in an unordered list. I've literally copied the code straight out of book just to be sure that I wasn't making any mistakes but the issue still exists.
 
Heres the code:
HTML:
///////////////
<body>
<div id="container">
 <div id="header">
    <div id="hiddenHeader"><img src="Jquery.png" width="780" height="150" /></div>
    <!-- Header that hides -->
  </div><!-- End Header -->
      <div id="contentBg">
         <ul id="navigation">
         <li><a href="#">Test</a></li>
         <li><a href="#">Test</a></li>
         <li><a href="#">Test</a></li>
         </ul>
        </div> <!-- Content BG End -->
</div> <!-- End Container -->
</body>













////////////////
 
CSS:
//////////////////
ul#navigation {
 position:relative;
 }
div#navigation_blob {
position:relative;
 }




//////////////////
JS:
/////////////////
$(function() {
 $('<div id="navigation_blob"></div>')
 .css({ width: $('#navigation li:first a').width() + 10,
 height: $('#navigation li:first a').height() + 10,
        'background-color': '#FFFFFF'})
 .appendTo($('#navigation')); // Creates nav blob
 $('#navigation a').hover(function() {
 $('#navigation_blob')
  .animate({width: $(this).width() + 10, left: $(this).position().left},
  {duration: 'slow', easing: 'easeOutElastic', queue: 'false'});
}, function() {
    $('#navigation_blob')
  .stop(true)
  .animate({width: 'hide'},
                {duration: 'slow', easing: 'easeOutCirc', queue: 'false'})
  .animate({left: $('#navigation li:first a').position().left}, 'fast');
})
});
















////////////////
 
The main issue here is that the highlight div '#navigation_blob' never goes underneath the links. The only action I can achieve from it is making it shoot all the way to the right of the screen and back on mouseover/mouseout. Every other parameter functions correctly except for this. I also followed a suggestion to use the css.offset().left function, yet that did not help the situation at all. How can I overlay this div underneath the links in the unordered list?
 
Thanks in advance!
 
IPS