[MarcelL94]

What

• Theme switcher in the sidebar, above "Support the project": it starts on "Windows theme" (follows Windows), and each click goes Windows theme → the opposite of Windows' look → Windows' look kept fixed → back to Windows theme (Windows' look is read from AppsUseLightTheme). The choice applies immediately and is kept in window.json (WindowPreferences.Theme, stored by name; older files without it keep following Windows).
• Dark mode text fix: the SidebarLink, ChoiceCard and Switch styles replace Fluent's implicit style for their control, so the classic theme's black Foreground showed through on dark backgrounds (e.g. "Support the project", the quality preset cards, the switch labels). They now set TextFillColorPrimaryBrush themselves.

Changes

• Gui/AppTheme.cs (new): AppTheme enum, ThemeChoice (label, glyph, the next one in the cycle), mapping to WPF ThemeMode, WindowsTheme (reads whether Windows shows apps light or dark).
• Gui/ViewModels/MainViewModel.cs: Theme preference, Theme / ChangeTheme for the sidebar button.
• Gui/App.xaml.cs: applies the saved theme at startup.
• Gui/MainWindow.xaml: the sidebar button.
• Gui/Theme.xaml: Foreground on the three styles.
• tests/AppThemeTests.cs (new): theme mapping, the click cycle for a light and a dark Windows, window.json round-trip.

Testing

dotnet build (no warnings) and dotnet test --solution OrthoStreamXP.slnx: 372 passed.

Notes

• The flight-report charts read their brushes when they render, so after a switch they keep the old colours until they next redraw.
• The README asks for PRs against develop, but that branch doesn't exist, so this targets main.

🤖 Generated with Claude Code

[flysimdev]

Hello @MarcelL94, First of all, thanks a lot for your contribution. I really appreciate your support.
Also, I want to ask you to implement the possibility of switching back to the default behavior (switching back to auto mode, which follows the Windows theme)

[MarcelL94]

Thanks for the review! Switching back to the default behaviour is now possible: the theme button is a 3-step cycle, so users can always return to following Windows.

1. Windows theme: follows the Windows setting (the default)
2. The opposite of Windows' look: e.g. Dark when Windows is Light
3. Windows' look, kept fixed: e.g. Light, even if Windows changes later

The next click goes back to Windows theme. Every click from the default changes the colours straight away, and the choice is kept in window.json across restarts.

[flysimdev]

@MarcelL94 Your improvement will go to the v1.2.1 release, as well as a bug fix related to the issue you posted.
Thanks one more time