https://drafts.csswg.org/css-conditional-5/#scroll-state-container

Describes:

The syntax of a <scroll-state-feature> is the same as for a media feature: a feature name, a comparator, and a value.

But that isn't the syntax of a media feature.
A media feature can also be only a name for example.

Given that all currently defined features are all discrete it might be better to define the syntax explicitly as:

<scroll-state-feature> = <ident> : <ident>