CheckBox and RadioButton with Appearance.Button and FlatStyle.Standard do not use the system accent color when checked in Dark Mode #15126

.NET version

.NET 11 RC2 build + integration/11.0-RC2 branch of Winforms repo

Did it work in .NET Framework?

Not tested/verified

Did it work in any of the earlier releases of .NET Core or .NET 5+?

NET11 new APIs

Issue description

When CheckBox or RadioButton is configured with Appearance = Button and FlatStyle = Standard, the checked state does not use the system accent color in Dark Mode.

In non-Dark Mode, the checked state is rendered with the expected system accent color.

Steps to reproduce

1. Create a WinForms application targeting .NET 11.
2. Set VisualStylesMode to VisualStylesMode.Net11.
3. Add a CheckBox and a RadioButton to the Form.
4. Set the following properties for both controls:

• Appearance = Button
• FlatStyle = Standard

6. Enable Dark Mode by adding code: Application.SetColorMode(SystemColorMode.Dark);
7. Run the application and check the CheckBox and RadioButton.
8. Observe the background color of the controls in the checked state