Unfortunately Gmail for iOS does not respect the <style> block that desktop
Gmail does. Styles are instead defined in a styles.json and can be referenced
via a custom template function. Not quite as nice as CSS (e.g. link style
invocation has to be repeated for every link), but still tolerable.
Not the final design (it'll instead be persisted to the App Engine data store,
and the session will just have the user ID), but this has most of the
scaffolding for session cookies.
