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.
background-opacity
; considering functionality for future specs, but probably not in that form. (See previous discussions on targetting filters.)box-break: continuous | each-box
will be renamed box-decoration-break: slice | clone
unless there is consensus on a better proposal.