It seems like some of the gin CSS variables are not defined when using the gin theme compatibility setting. It is working only if you are using the gin_toolbar module in addition of layout_builder_quick_add
Fixed
1.0
Code
Issue #3416605 by phjou: Gin style missing dependency when not using...
Similar technique as gin_toolbar has been used to fix the issue.
Automatically closed - issue fixed for 2 weeks with no activity.