[FIX] Port old code in csslib to ThemeLib. Fixes layouts not being available...
- [FIX] Port old code in csslib to ThemeLib. Fixes layouts not being available for themes in _custom, and other places
(cherry picked from commit dfb5cd56), from MR !4945 (merged)
Co-authored-by: Benoit Grégoire benoitg@coeus.ca