This is a page from the Cascading Style Sheets Working Group Blog. Some other places to find information are the “current work” page, the www-style mailing list, the Future of CSS syndicator, and the issue list on Github.
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.
@document
to Level 4 due to open issues.
@import
syntax for @supports
queries due to lack of proposal.
clip
property into the Masking module.
@counter-style
rules.