ComboBox with FlatStyle.System renders incorrectly at design time

[Amy-Li03]

.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?

Yes

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

Not support, new feature

Issue description

The ComboBox is rendered incorrectly in the designer when FlatStyle.System is used together with VisualStylesMode.Net11.

Steps to reproduce

1. Create a WinForms .NET application
2. Set VisualStylesMode to Net11
3. Add a ComboBox to form designer
4. Set the ComboBox's FlatStyle as System
5. Observe the ComboBox rendering