When I uploaded my .css file to valide it, it said:

No error or warning found

To work as intended, your CSS style sheet needs a correct document parse tree. This means you should use valid HTML.

That's where I stuck. I validated my HTML and I got:

This Page Is Valid HTML 4.01 Transitional!

But why won't it validate my CSS if it says no errors or warnings found? :confused:

If it says that no error or warning was found, it should be valid in itself. The part about HTML just means that it's pointless to validate your CSS if your HTML is not valid.

The best would be to post your stylesheet here, if it's not the one currently in use at your site.