problem positioning a hotspot over an image

I'm having a problem positioning a hotspot (should be a rectangle 230px wide by 88px high) over an image in a web page header.  Rather than appearing over top of the image using the coordinates defined in the CSS, it displays right before the image.  What am I doing wrong?

Here's what I have:

HTML

<div class="art-Header">
    <jdoc:include type="modules" name="Search-box" />
    <div class="art-Header-jpeg">
            <a href="http://www.agro-k.com/index.php?option=com_alfcontact&Itemid=148" class="hotspot" title="Contact Us">&nbsp</a>
      </div>
</div>

CSS

div.art-Header-jpeg
{
      position: absolute;
      z-index:-1;
      top: 30;
      left: 0;
      width: 906px;
      height: 150px;
      background-image: url('../images/Header.png');
      background-repeat: no-repeat;
      background-position: center center;
}


div.art-Header-jpeg .hotspot a
{
    width: 130px; height: 88px;
    position: absolute;
    top: 567px; /* Top coord of hotspot (relative to parent, bottom: 20px is also valid) */
    left: 44px; /* Left coord of hotspot (right: 20px is also valid); */
      z-index:100;
}