When I was using QtCreator 13.0.0 my code editor was in dark mode (as configured) and the widget designer in light mode (by default - not configurable).

Since I updated to 15.0.0, the widget designer is also in dark mode and seems to be following the theme of my computer (dark mode - gnome - ubuntu20). It's very difficult to design UI in dark mode as I can't see layouts borders, shapes, etc correctly.

Is there a functionality to switch widget designer theme independently from my OS and code editor themes ?

This could also be beneficial to see the look of the GUI in both modes at any moment.