The application is using WinForms MDI. This has a reported issue that MDI forms use Windows 7 styles while dialogs and forms outside of the MDI container use the OS defined style. This causes inconstancies in the appearance of some windows.
This is not something that can be fixed by the developer. It is an issue within Windows itself. Apparently, Microsoft failed to update the images and other components for newer OS's.
Rework the entire UI using WPF. This has its own issues beyond just the learning curve. The goal would be to created a tabbed UI similar to how many browsers work.
Make all windows appear inside the MDI. Dialog screens are specifically an issue. By there nature they appear on top of everything else and are model. This could cause issues with how forms are enabled and disabled.
Jury-rig the forms to look like Windows 10. A couple of third party tools do this but the basic trick is to re-do how everything gets painted. This also has to some-how read the style from the OS. Otherwise, the style becomes hard-coded and we are back to the same issue.
The application is using WinForms MDI. This has a reported issue that MDI forms use Windows 7 styles while dialogs and forms outside of the MDI container use the OS defined style. This causes inconstancies in the appearance of some windows.
This is not something that can be fixed by the developer. It is an issue within Windows itself. Apparently, Microsoft failed to update the images and other components for newer OS's.
MDI child windows use hard-coded Visual Style Rendering
Ideas
Otherwise, I just have to live with it.