Changing cache file extension for select output

Hello – I’m working on an app that, among other things, allows users to
customize the look of their sites by creating/editing css code; at
present, each time one of their pages is rendered, the css is drawn from
the DB and put together on the fly. For obvious reasons, I would really
like to cache this action (as a .css file).

My challenge is that I’m unsure how to cache these actions as .css files
without breaking the standard “.html” caching extension that I want to
use in other places. Any guidance you can offer here would be a huge
help.

Thanks,
Dieter