Help Validating

Hello,
I have been trying to validate by css style sheet but to no avail. The message I receive says that my document contains no errors or warnings. Yet it says, "To work as intended, your CSS style sheet needs a correct document parse tree. This means you should use valid html." However, my website validates perfectly using XHTML 1.0. Please help me to understand! 

P.S. When I use the link to validate my web site as CSS I get an error message!