dotnet/winforms

[Dark Mode] The Form title bar is white color when the MDIParent1 MainMenuStrip property is set to none

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#12,991 opened on Feb 20, 2025

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area-DarkModehelp wanted

Description

.NET version

.NET 10.0.100-preview.2.25118.3

Did it work in .NET Framework?

No

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

No, also repro in .NET 9.0 which it started to be supported.

Issue description

The Form title bar is white color when the MDIParent1 MainMenuStrip property is set to none.

Image

https://github.com/user-attachments/assets/f0a3ce9b-9f6f-45a0-a14f-52be1c43d662

Steps to reproduce

  1. Create a winforms .NET Core project.
  2. Enable DarkMode by Application.SetColorMode(SystemColorMode.Dark) in Program.cs file.
  3. Ctrl+Shift+A to add a MDI Parent Form.
  4. Set MDIParent1 MainMenuStrip property to none.
  5. Build and run MDIParent1.
  6. Click File -> New, select Window0's Maximize button.

More Info:

  1. This issue also repro when click MDI Parent button in WinformsControlTest app.

Image

Contributor guide

Tech stack
csharp
Domain
desktop
Issue type
bug
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
3
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
half day
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
blocked
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
clear
Prerequisites
C#Windows FormsDark mode themingMDI
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
40
Research direction
This issue relates to the dark mode title bar color when MainMenuStrip is null. Investigate the rendering logic in the Form's title bar and MDI client area, possibly in files such as 'Form.cs' or 'MdiClient.cs' within the System.Windows.Forms source. Review the existing dark mode implementation and check how the title bar color is determined when MainMenuStrip is not set. Look at recent changes related to dark mode in the repository to identify the root cause.