Address review: handle HighContrast themes in initial ThemeMode selection

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: MuyuanMS

src/modules/launcher/PowerLauncher/App.xaml.cs

@@ -154,17 +154,13 @@ private void OnStartup(object sender, StartupEventArgs e)
 
                 _mainVM = new MainViewModel(_settings, NativeThreadCTS.Token);
 
-                // Set ThemeMode before MainWindow creation so Fluent static resources
-                // (e.g. DefaultTextBoxStyle, CaptionTextBlockStyle) are available for XAML
-                // parsing. ThemeManager will apply the correct final theme asynchronously.
-                // For high-contrast themes, Dark is used as a temporary fallback because
-                // ThemeManager will switch to ThemeMode.None and apply custom high-contrast
-                // resource dictionaries once it processes the actual theme. Dark is chosen
-                // because the high-contrast themes are visually closer to dark than light.
+                // Set ThemeMode before MainWindow creation so the initial theme state is
+                // consistent with ThemeManager. This avoids preloading Dark Fluent resources
+                // when Windows starts in a High Contrast theme.
                 var themeHelper = new ThemeHelper();
                 var initialTheme = themeHelper.DetermineTheme(_settings.Theme);
 #pragma warning disable WPF0001
-                Application.Current.ThemeMode = initialTheme == Theme.Light ? ThemeMode.Light : ThemeMode.Dark;
+                Application.Current.ThemeMode = ThemeManager.GetThemeMode(initialTheme);
 #pragma warning restore WPF0001
 
                 _mainWindow = new MainWindow(_settings, _mainVM, NativeThreadCTS.Token);

src/modules/launcher/PowerLauncher/Helper/ThemeManager.cs

@@ -32,6 +32,15 @@ public class ThemeManager : IDisposable
 
         public event Common.UI.ThemeChangedHandler ThemeChanged;
 
+        internal static ThemeMode GetThemeMode(Theme theme) => theme switch
+        {
+            Theme.Light => ThemeMode.Light,
+            Theme.Dark => ThemeMode.Dark,
+            Theme.HighContrastBlack or Theme.HighContrastWhite or Theme.HighContrastOne or
+                Theme.HighContrastTwo => ThemeMode.None,
+            _ => ThemeMode.Dark,
+        };
+
         public ThemeManager(PowerToysRunSettings settings, MainWindow mainWindow)
         {
             _settings = settings;
@@ -65,7 +74,7 @@ private void SetSystemTheme(Theme theme)
                 // Need to disable WPF0001 since setting Application.Current.ThemeMode is experimental
                 // https://learn.microsoft.com/en-us/dotnet/desktop/wpf/whats-new/net90#set-in-code
 #pragma warning disable WPF0001
-                Application.Current.ThemeMode = theme == Theme.Light ? ThemeMode.Light : ThemeMode.Dark;
+                Application.Current.ThemeMode = GetThemeMode(theme);
 #pragma warning restore WPF0001
 
                 if (!OSVersionHelper.IsWindows11())
@@ -83,7 +92,7 @@ private void SetSystemTheme(Theme theme)
                 // For high-contrast themes, disable WPF's Fluent theme manager to avoid conflicts
                 // with the custom high-contrast resource dictionaries.
 #pragma warning disable WPF0001
-                Application.Current.ThemeMode = ThemeMode.None;
+                Application.Current.ThemeMode = GetThemeMode(theme);
 #pragma warning restore WPF0001
 
                 _isHighContrastMode = true;

src/modules/launcher/Wox.Test/ThemeManagerTest.cs

@@ -0,0 +1,26 @@
+// Copyright (c) Microsoft Corporation
+// The Microsoft Corporation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+using System.Windows;
+using ManagedCommon;
+using Microsoft.VisualStudio.TestTools.UnitTesting;
+using PowerLauncher.Helper;
+
+namespace Wox.Test;
+
+[TestClass]
+public class ThemeManagerTest
+{
+    [DataTestMethod]
+    [DataRow(Theme.Light, ThemeMode.Light)]
+    [DataRow(Theme.Dark, ThemeMode.Dark)]
+    [DataRow(Theme.HighContrastBlack, ThemeMode.None)]
+    [DataRow(Theme.HighContrastWhite, ThemeMode.None)]
+    [DataRow(Theme.HighContrastOne, ThemeMode.None)]
+    [DataRow(Theme.HighContrastTwo, ThemeMode.None)]
+    public void GetThemeMode_ReturnsExpectedThemeMode(Theme theme, ThemeMode expectedThemeMode)
+    {
+        Assert.AreEqual(expectedThemeMode, ThemeManager.GetThemeMode(theme));
+    }
+}