Stacking problem in IE7

I read an old post on this site about fixing a IE7 bug (see below) that said:

“On hover, my CSS sub-menu appears behind other page elements below. For example, Products sub-menu is behind the title and thumbnails.”

I am having the same problem (but my knowledge is minimal).

You’re suggestion was to:
“Place z-index:2 on ul#main-nav to fix it.”

I was wondering if you could tell me if I add the z-index:2 code to my html page or css page?

It would be to the css page. If you wanted that to be on top all the time then I would use a higher z-index as in

z-index: 99;

then you know that will always appear on top.