Fix window caption buttons invisible in Light theme

CHANGELOG.md

@@ -17,6 +17,12 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
   remove icons (the picker reflects the change the next time it opens), and your
   edits survive app updates. Delete it to restore the default set.
 
+### Fixed
+- **Window caption buttons invisible in Light theme.** The minimise, maximise and
+  close glyphs were always white, leaving them barely visible against the light
+  title bar. They now take a theme-appropriate colour, update when you switch
+  theme, and follow the OS when the theme is set to System.
+
 ### Changed
 - **Home, navigation and shared-parameters polish.** The Home page leads with a
   full-bleed hero banner (drop `Assets/HomeHero.png` to supply the image), the

src/Snipdeck.App/MainWindow.xaml.cs

@@ -35,6 +35,14 @@ public MainWindow(AppConfig config, ShellPage shellPage)
             ShellHost.Content = shellPage;
 
             ApplyTheme(config.Theme);
+
+            // While on System theme, the caption buttons must follow an OS
+            // light/dark flip too — RequestedTheme stays Default, so only
+            // ActualTheme changes.
+            if (Content is FrameworkElement themedRoot)
+            {
+                themedRoot.ActualThemeChanged += (sender, _) => UpdateCaptionButtonColours(sender.ActualTheme);
+            }
         }
 
         // The title-bar switcher and snip search bind to the shell view model.
@@ -129,18 +137,61 @@ private void OnSearchQuerySubmitted(AutoSuggestBox sender, AutoSuggestBoxQuerySu
             }
         }
 
-        private void ApplyTheme(ThemePreference theme)
+        /// <summary>
+        /// Applies the chosen theme to the app content and the system caption
+        /// buttons. Public so the runtime theme applier routes through here,
+        /// keeping the window content and the min/max/close glyphs in step.
+        /// </summary>
+        public void ApplyTheme(ThemePreference theme)
         {
-            if (Content is FrameworkElement root)
+            if (Content is not FrameworkElement root)
             {
-                root.RequestedTheme = theme switch
-                {
-                    ThemePreference.Light => ElementTheme.Light,
-                    ThemePreference.Dark => ElementTheme.Dark,
-                    ThemePreference.System => ElementTheme.Default,
-                    _ => ElementTheme.Default,
-                };
+                return;
             }
+
+            root.RequestedTheme = theme switch
+            {
+                ThemePreference.Light => ElementTheme.Light,
+                ThemePreference.Dark => ElementTheme.Dark,
+                ThemePreference.System => ElementTheme.Default,
+                _ => ElementTheme.Default,
+            };
+
+            // ActualTheme resolves Default to the OS light/dark choice, so the
+            // caption glyphs get a concrete theme to contrast against.
+            UpdateCaptionButtonColours(root.ActualTheme);
+        }
+
+        // The caption buttons are system-drawn chrome, not styled by the app's
+        // theme resources — so without this they keep their default (white)
+        // glyphs and vanish on a light background. Backgrounds stay transparent
+        // so the Mica backdrop shows through; only the glyph colours change.
+        private void UpdateCaptionButtonColours(ElementTheme actualTheme)
+        {
+            var dark = actualTheme == ElementTheme.Dark;
+
+            var foreground = dark
+                ? Microsoft.UI.Colors.White
+                : Windows.UI.Color.FromArgb(0xFF, 0x1A, 0x1A, 0x1A);
+            var inactive = dark
+                ? Windows.UI.Color.FromArgb(0xFF, 0x80, 0x80, 0x80)
+                : Windows.UI.Color.FromArgb(0xFF, 0x8A, 0x8A, 0x8A);
+            var hoverBackground = dark
+                ? Windows.UI.Color.FromArgb(0x1F, 0xFF, 0xFF, 0xFF)
+                : Windows.UI.Color.FromArgb(0x14, 0x00, 0x00, 0x00);
+            var pressedBackground = dark
+                ? Windows.UI.Color.FromArgb(0x12, 0xFF, 0xFF, 0xFF)
+                : Windows.UI.Color.FromArgb(0x0A, 0x00, 0x00, 0x00);
+
+            var titleBar = AppWindow.TitleBar;
+            titleBar.ButtonBackgroundColor = Microsoft.UI.Colors.Transparent;
+            titleBar.ButtonInactiveBackgroundColor = Microsoft.UI.Colors.Transparent;
+            titleBar.ButtonForegroundColor = foreground;
+            titleBar.ButtonHoverForegroundColor = foreground;
+            titleBar.ButtonHoverBackgroundColor = hoverBackground;
+            titleBar.ButtonPressedForegroundColor = foreground;
+            titleBar.ButtonPressedBackgroundColor = pressedBackground;
+            titleBar.ButtonInactiveForegroundColor = inactive;
         }
     }
 }

src/Snipdeck.App/Services/WindowsThemeApplier.cs

@@ -1,5 +1,3 @@
-using Microsoft.UI.Xaml;
-
 using Snipdeck.Core.Abstractions;
 using Snipdeck.Core.Models;
 
@@ -17,17 +15,10 @@ public WindowsThemeApplier(IServiceProvider services)
 
         public void Apply(ThemePreference theme)
         {
+            // Route through the window so the content and the system caption
+            // buttons are themed together (see MainWindow.ApplyTheme).
             var mainWindow = (MainWindow?)_services.GetService(typeof(MainWindow));
-            if (mainWindow?.Content is FrameworkElement root)
-            {
-                root.RequestedTheme = theme switch
-                {
-                    ThemePreference.Light => ElementTheme.Light,
-                    ThemePreference.Dark => ElementTheme.Dark,
-                    ThemePreference.System => ElementTheme.Default,
-                    _ => ElementTheme.Default,
-                };
-            }
+            mainWindow?.ApplyTheme(theme);
         }
     }
 }