CSS2 - Validator

Dear Sir,

Is it required that when creating a linked style sheet (.css file) that you
use a document parse tree.  I am asking this because my styles.css document
has no errors / warnings in it, but I still am not offered the W3C CSS Logo.

Any help on this topic would be great.

Yours faithfully,

Thomas O'Connor
toconnor88@bigpond.com
www.austamps.cjb.net