[css-values-5] Disallow mix/random/tree-counting functions in some contexts

[chromium-helper]

CSSWG added the following resolution(s):

• RESOLVED: Explicitly allow tree-counting functions in container queries

in w3c/csswg-drafts#10982 (comment)

[chromium-helper]

I have filed issues.chromium.org/419273125

That is all that can be done here, closing issue.