Do you want to know how the CSS WG works? Fantasai has written about:csswg, An Inside View of the CSS Working Group at W3C.
The CSSWG has published an updated Candidate Recommendation of the CSS Backgrounds and Borders Module Level 3. Changes since the last CR are mostly correcting errors and clarifications, and are detailed in the Changes section. A Disposition of Last Call Comments is also available.
W3C encourages everybody to implement this specification and return comments to the (archived) public mailing list firstname.lastname@example.org (see instructions). When sending e-mail, please put the text
[css3-background] in the subject (alternatively you can email one of the editors and ask them to forward your comment).