Missing classic theme in 4.4.4091.6409

After upgrading the test environment to Application Workspace 4.4.4091.6409 I am missing the Classic theme, and I have a white left pane again which can't be modified.

I tried copying the classic theme over from 4.3 but that doesn't work unfortunately. This is a recurring request for every major upgrade in the past few years.

This will be a big thing for my users.

I would appreciate to have the classic theme back or else be able to modify the left pane in the default theme.

Thanks.