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.
visibility during a transition between hidden/visible and collapse/visible is visible; between hidden/collapse is non-interpolable.
to syntax for linear-gradient(), and only that syntax, because it’s adequate and has been tweaked too much already.