下拉菜单显示在主菜单的上面怎么做
要求子菜单显示在主菜单的上面，而不是下面，用这段代码一直是显示在下面。
要怎么做才能在上面显示啊。


<script language="javascript">
  startList = function () {
  if (document.all && document.getElementById) {
  navRoot = document.getElementById("nav");
  for (i = 0; i < navRoot.childNodes.length; i++) {
  node = navRoot.childNodes[i];
  if (node.nodeName == "SPAN") {
  node.onmouseover = function () { this.className += " over"; }
  node.onmouseout = function () { this.className = this.className.replace(" over", ""); }
  }
  }
  }
  }
  window.onload = startList;
</script>

<style type="text/css">
body {
background-color: #FFFFFF;
margin-left: 0px;
margin-top: 0px;
margin-right: 0px;
margin-bottom: 0px;
}

div#nav{
  height:200px;
}
span {
  margin: 0px;
  padding: 0px;
  list-style: none;
  width: 200px; /* Width of Menu Items */
  position: relative;
  border: 0px;
}
span div span {
  border: 0px;
  border-top: 0px;
}
span div {
  position: absolute;
  left: -1px;
  display: none;
}

/* Styles for Menu Items */
div span a {
  width: 100%;
  text-decoration: none;
  color: #777;
  background: #fff; /* IE6 Bug */
  padding: 5px;
}

div span a:hover { color: #2E5B89; background: #DFF8FF; } /* Hover Styles */
   
span div span a { padding: 2px 5px; } /* Sub Menu Styles */
   
span:hover div, span.over div { display: inline; } /* The magic */
</style>
   
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