.NET version
.NET SDK 9.0.100-rc.1.24415.1 + build private dll form winforms repo release/9.0 branch
Did it work in .NET Framework?
No
Did it work in any of the earlier releases of .NET Core or .NET 5+?
This is a new feature Dark Mode: #11857
Issue description
Control pops up dialogs and MessageBox window are not in Dark mode when DarkMode enabled
ColorDialog:

FontDialog:

MessageBox:

Steps to reproduce
- Create a WinForms .NET Core application.
- Enable DarkMode by
Application.SetColorMode(SystemColorMode.Dark) in program.cs file.
- Add three button controls to the form designer.
- Add click events to open FontDialog, ColorDialog and MessageBox for each of the three buttons.
- Run the application.
- Click each of the three buttons and observe the color of the new dialog.