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.
@page
declarations that size the initial containing block. Also discussed whether such units are resolved at computed value time (relative to ICB) or used value time (relative to the page). Plan to ask for feedback from CSS-to-print/PDF implementers, since they have more experience / use cases than browser vendors do.
@supports
to make invalid parenthesized expressions also evaluate to false, rather than invalidating the rule.