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On Windows 11 25H2 with Dark Mode enabled, the ProgressBar control renders with incorrect/ugly appearance when ProgressBarStyle is changed at runtime. The OS automatically applies the DarkMode_Explorer theme (one of the new ProgressBar themes introduced in 25H2), which does not look good on WinForms ProgressBar.
Specific cases:
Works fine: Blocks at design time → change to Marquee at runtime.
Broken:
Blocks at design time → change to Continuous at runtime.
Any style set at design time (Marquee or Continuous) → changed at runtime.
Expected behavior
ProgressBar should have clean, consistent Dark Mode styling for all ProgressBarStyle values, regardless of design-time or runtime changes.
Actual behavior
Broken/ugly visuals (bad colors, incorrect fill, etc.) due to improper handling of the new DarkMode_Explorer theme.
Additional context
No manual SetWindowTheme() is called from the application.
Windows 11 25H2 introduced new DarkMode themes for ProgressBar: DarkMode_CopyEngine, DarkMode_DarkTheme, and DarkMode_Explorer.
You can inspect these themes using this tool: aero-darkmode-parser
Use the attached minimal project on Windows 11 25H2 (Dark Mode enabled).
Run the app.
Click Start — it will cycle through the styles at runtime.
Pay special attention when it switches to Continuous.
.NET version
.net 9 and newer
Issue description
On Windows 11 25H2 with Dark Mode enabled, the ProgressBar control renders with incorrect/ugly appearance when ProgressBarStyle is changed at runtime. The OS automatically applies the DarkMode_Explorer theme (one of the new ProgressBar themes introduced in 25H2), which does not look good on WinForms ProgressBar.
Specific cases:
Works fine: Blocks at design time → change to Marquee at runtime.
Broken:
Blocks at design time → change to Continuous at runtime.
Any style set at design time (Marquee or Continuous) → changed at runtime.
Expected behavior
ProgressBar should have clean, consistent Dark Mode styling for all ProgressBarStyle values, regardless of design-time or runtime changes.
Actual behavior
Broken/ugly visuals (bad colors, incorrect fill, etc.) due to improper handling of the new DarkMode_Explorer theme.
Additional context
No manual SetWindowTheme() is called from the application.
Windows 11 25H2 introduced new DarkMode themes for ProgressBar: DarkMode_CopyEngine, DarkMode_DarkTheme, and DarkMode_Explorer.
You can inspect these themes using this tool: aero-darkmode-parser
Steps to reproduce
Steps to reproduce
WinFormsApp1.zip
Use the attached minimal project on Windows 11 25H2 (Dark Mode enabled).
Run the app.
Click Start — it will cycle through the styles at runtime.
Pay special attention when it switches to Continuous.
Recording.2026-05-20.095837.mp4
Version Information
OS: Windows 11 25H2 Build 26220.6772 and newer