Standardizing Host CSS Variables

[rabisg]

Hey team,
Wanted to understand the future of CSS variables https://github.com/modelcontextprotocol/ext-apps/blob/main/src/spec.types.ts better. Given that there aren't a lot of globally agreed upon conventions for these variables (names & intent) - do you see them stabilising in the future across different hosts or should app builders consider all of them as optional and handle it accordingly?

[liady]

Hi @rabisg, this is a good question.
The spec defines these variables as the standardized set, and specifies that hosts may only pass a subset of it (see here) - so apps should have appropriate fallbacks for all of them.
I agree that this might create edge cases where an app that expects related variables to "play" together (to either be defined by the host, or to have the fallback values) might eventually have a mix of host-defined and fallback values. But currently the apps assumption should be that hosts may provide only a subset of the values (or none at all).
Do you see additional issues here?

[rabisg]

No issues but would love to see more documentation around it as we adopt it. We're happy to contribute in any way too

Just defining the variables - what they mean in a more illustrative format (like shadcn variables) would be a good starting point imo. Wdyt?