DataGridViewComboBoxCell has multiple layout issues when entering edit mode

[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?

Not tested/verified

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, the embedded ComboBox editor used by DataGridViewComboBoxCell exhibits several layout/rendering issues while editing:

• The rounded drop-down button is shifted to the left instead of aligning with the right edge of the editor.
• An unexpected vertical scrollbar appears to the right of the drop-down button.
• The drop-down list is slightly offset from the editing control instead of opening flush beneath it.

These issues make the embedded ComboBox editor appear misaligned and visually inconsistent.

DataGridViewComboBoxIssue.mp4

Steps to reproduce

1. Create a new WinForms application targeting .NET 11.
2. Set the Form's VisualStylesMode to NET11.
3. Add a DataGridView to the Form.
4. Add a DataGridViewComboBoxColumn and populate it with several items.
5. Run the application.
6. Click a cell in the DataGridViewComboBoxColumn to enter edit mode.
7. Open the drop-down list.

[KlausLoeffelmann]

Whoopsidaisies!
Yep - need to take a look...

[Olina-Zhang]

Tested in the branch: Integration-4, the DataGridViewComboBox doesn't display completely in cell: