[jss-template] Nesting, etc?

__Is your feature request related to a problem? Please describe.__

Can we nest rules when using jss-template? If so, how?

__Describe the solution you'd like__

If not, this would be nice.

__Are you willing to implement it?__

No time to at the moment.

Start by examining the jss-template implementation and its documentation to determine whether nested rules are currently supported. Define the expected nesting behavior and usage before deciding what implementation and verification would be needed; the issue does not name specific files or tests.

Written by the indexing model from the issue text.