The CSS Working Group has published the CSS Snapshot 2021. This Working Group Note indexes all the CSS specifications that are reasonably complete or stable as of 2021. (You can also find a complete list of all our specifications, including those unstable and in progress, on the current work page.) The latest snapshot is also always available at w3.org/TR/CSS/.
As usual, you can send feedback by either filing an issue in GitHub (preferable) or sending mail to the (archived) public mailing list www-style@w3.org with the spec code ([css-2021]) and your comment topic in the subject line. (Alternatively, you can email one of the editors and ask them to forward your comment.)