Aha, this is related to bug 1899295 it looks like. That bug is about `from(light-dark(...` at least. Marking this as depending-on that one, rather than a duplicate, since it's not clear to me whether this is entirely the same vs. if the behavior with the CSS-variable-expansion is another distinct layer of brokenness per comment 2.
Bug 1907843 Comment 3 Edit History
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Aha, this is related to bug 1899295 it looks like. That bug is about `from light-dark(...` at least. Marking this as depending-on that one, rather than a duplicate, since it's not clear to me whether this is entirely the same vs. if the behavior with the CSS-variable-expansion is another distinct layer of brokenness per comment 2.