Button hosted on a TabPage does not use the Windows accent-colored focus indicator with VisualStylesMode = NET11

[Olina-Zhang]

.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 of #14768

Issue description

When VisualStylesMode is set to NET11, a Button correctly uses the Windows accent-colored focus indicator when hosted directly on a Form or on other common container controls: Panel, GroupBox, FlowLayoutPanel, TableLayoutPanel, SplitContainer.Panel.
However, when the same Button is hosted on a TabPage, it does not use the Windows accent color and instead falls back to the traditional focus rendering.
The behavior is inconsistent and appears to depend on the parent container.

Button in GroupBox:

Button in TabControl.TabPage:

Steps to reproduce

1. In Windows Settings > Personalization > Colors, select a noticeable Accent color (for example, Red).
2. Create a WinForms application targeting .NET 11.
3. Set the Form's VisualStylesMode to NET11.
4. Add:

• A Button directly on the Form.
• A TabControl containing a TabPage with another Button.

5. Run the application.
6. Focus both buttons using either the mouse or the keyboard.