Sub-theme of a sub-theme If you have a sub-theme of a sub-theme...


Sub-theme a
Sub-theme b (base theme = Sub-theme a)


Ideally, what I want to do is have the default theme as 'Sub theme a' and just introduce some minor theming and processing in 'Sub theme b'. Reason being, there are lots of versions of this site being deployed and some minor fixes are required that can be thrown away at the click of a button i.e. remove Sub-theme b.

Google has not been helpful in this instance ;-)

If both themes are enabled and sub-theme a is the default, how do I get sub-theme b to work? (because its not working i.e. I have added a stylesheet in the .info file and its not being added. If I make sub-theme b default then Sub-theme a doesnt work)
You always start with a base-theme.  Let us call this Theme A.  If you introduce a sub-theme (e.g. Theme B as a sub-theme of Theme A), it inherits everything from Theme A.  You can introduce minor (or major) tweaks in Theme B.

If you set Theme B as the default, then you get Theme A + Theme B.

If you set Theme A as the default, then you get Theme A (with nothing from Theme B).

In other words, if you've set Theme A as the default, then Theme B is not supposed to work.   To get Theme B to "work", you must set Theme B as the default.

This also works if you cascade with more sub-themes.

For instance, if you introduce another sub-theme (e.g. Theme C as a sub-theme of Theme B), it inherits everything from Theme A and Theme B. You can then introduce minor (or major) tweaks in Theme C.

If you set Theme C as the default, then you get Theme A + Theme B  + Theme C.

A theme need to be enabled to be set as default, but works fine as an inherited theme even when it is not enabled.