GroupBox does not render BackgroundImage correctly when FlatStyle is Standard, Popup, or System with VisualStylesMode.Net11 mode

[Amy-Li03]

.NET version

.NET 11.0.100-preview.7.26365.114 + Private dlls built from Net11/Integration-3 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

In VisualStylesMode.Net11 mode design time and run time, GroupBox.BackgroundImage is not rendered correctly when the control uses FlatStyle.Standard/Popup/System values. BackgroundImage is painted over child control(Button) borders in System FlatStyle mode
The background image is only rendered correctly when FlatStyle.Flat is used.

Behavior from VisualStylesMode.Classic:

Steps to reproduce

1. Create a WinForms application targeting .NET 11
2. Set VisualStylesMode = VisualStylesMode.Net11
3. Add several GroupBoxs to form designer with BackGroundImage
4. Configure different FlatStyle values: Standard/Popup/System