这个单元格的样式如何实现呀

<style>
.t1 {background: menu}
.t2 {background: white}
.tt {background: highlight; color: highlighttext;}
</style>
<table border=1 id=tab1 width=400>
<tr><td>aaa</td><td>bbb</td></tr>
<tr><td>aaa</td><td>bbb</td></tr>
<tr><td>aaa</td><td>bbb</td></tr>
<tr><td>aaa</td><td>bbb</td></tr>
<tr><td>aaa</td><td>bbb</td></tr>
<tr><td>aaa</td><td>bbb</td></tr>
</table><script language=javascript>
function mm()
{
   var a = document.all.tab1.getElementsByTagName("tr"), c;
   for (var i=0; i<a.length; i++)
   {
      c = (c=="t1") ? "t2" : "t1";
      a[i].className = c
   }
}  mm();
function document.onclick()
{
    mm();
   if(window.event.srcElement.tagName == "TD")
   {
      var e = window.event.srcElement.parentElement;
      e.className = "tt";
   }
}
</script>
Get some information here:
http://msdn.microsoft.com/library/en-us/dndude/html/dude07232001.asp?frame=trueTry this sample simply:
http://msdn.microsoft.com/library/en-us/dndude/html/qualhl.asp