CheckBox/RadioButton: ToggleSwitch renders black background when BackColor is Transparent

[Olina-Zhang]

.NET version

.NET 11.0.100-preview.7.26365.114 + Private dlls built from Net11/Integration-4 branch of https://github.com/KlausLoeffelmann/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+?

Not support, new feature of #14792

Issue description

When a CheckBox or RadioButton is configured with:

• Appearance = Appearance.ToggleSwitch
• BackColor = Color.Transparent
• Application.VisualStylesMode = VisualStylesMode.Net11

the control is rendered with an unexpected black rectangular background.

The ToggleSwitch glyph itself is painted correctly, but the control background is not rendered transparently as expected.

Steps to reproduce

1. Create a new WinForms application targeting .NET 11 Preview.
2. Enable VisualStylesMode to Net11;
3. Add a CheckBox or RadioButton to the form.
4. Set the following properties:

• Appearance = Appearance.ToggleSwitch
• BackColor = Color.Transparent

5. Run the application.

WinFormsApp179.zip