Update the default themes for 1.16

src/cascadia/TerminalApp/App.xaml

@@ -149,10 +149,13 @@
                                 See GH #12356 for more history on the subject.
                             -->
                             <SolidColorBrush x:Key="TabViewBackground"
-                                             Color="#0a0a0a" />
+                                             Color="#2e2e2e" />
 
                             <StaticResource x:Key="UnfocusedBorderBrush"
                                             ResourceKey="ApplicationPageBackgroundThemeBrush" />
+
+                            <SolidColorBrush x:Key="SettingsUiTabBrush"
+                                             Color="#0c0c0c" />
                         </ResourceDictionary>
 
                         <ResourceDictionary x:Key="Light">
@@ -162,10 +165,13 @@
                                 GH #12398 has more history on this value, as well as GH #12400
                             -->
                             <SolidColorBrush x:Key="TabViewBackground"
-                                             Color="#dadada" />
+                                             Color="#e8e8e8" />
 
                             <StaticResource x:Key="UnfocusedBorderBrush"
                                             ResourceKey="ApplicationPageBackgroundThemeBrush" />
+
+                            <SolidColorBrush x:Key="SettingsUiTabBrush"
+                                             Color="#ffffff" />
                         </ResourceDictionary>
 
                         <ResourceDictionary x:Key="HighContrast">
@@ -183,6 +189,9 @@
                             -->
                             <StaticResource x:Key="TabViewBackground"
                                             ResourceKey="SystemColorButtonFaceColorBrush" />
+
+                            <StaticResource x:Key="SettingsUiTabBrush"
+                                            ResourceKey="SystemControlBackgroundBaseLowBrush" />
                         </ResourceDictionary>
 
                     </ResourceDictionary.ThemeDictionaries>

src/cascadia/TerminalApp/SettingsTab.cpp

@@ -23,9 +23,11 @@ namespace winrt
 
 namespace winrt::TerminalApp::implementation
 {
-    SettingsTab::SettingsTab(MainPage settingsUI)
+    SettingsTab::SettingsTab(MainPage settingsUI,
+                             winrt::Windows::UI::Xaml::ElementTheme requestedTheme)
     {
         Content(settingsUI);
+        _requestedTheme = requestedTheme;
 
         _MakeTabViewItem();
         _CreateContextMenu();
@@ -36,6 +38,10 @@ namespace winrt::TerminalApp::implementation
     {
         auto settingsUI{ Content().as<MainPage>() };
         settingsUI.UpdateSettings(settings);
+
+        // Stash away the current requested theme of the app. We'll need that in
+        // _BackgroundBrush() to do a theme-aware resource lookup
+        _requestedTheme = settings.GlobalSettings().CurrentTheme().RequestedTheme();
     }
 
     // Method Description:
@@ -105,4 +111,16 @@ namespace winrt::TerminalApp::implementation
             TabViewItem().IconSource(IconPathConverter::IconSourceMUX(glyph));
         }
     }
+
+    winrt::Windows::UI::Xaml::Media::Brush SettingsTab::_BackgroundBrush()
+    {
+        // Look up the color we should use for the settings tab item from our
+        // resources. This should only be used for when "terminalBackground" is
+        // requested.
+        static const auto key = winrt::box_value(L"SettingsUiTabBrush");
+        // You can't just do a Application::Current().Resources().TryLookup
+        // lookup, cause the app theme never changes! Do the hacky version
+        // instead.
+        return ThemeLookup(Application::Current().Resources(), _requestedTheme, key).try_as<winrt::Windows::UI::Xaml::Media::Brush>();
+    }
 }

src/cascadia/TerminalApp/SettingsTab.h

@@ -24,15 +24,20 @@ namespace winrt::TerminalApp::implementation
     struct SettingsTab : SettingsTabT<SettingsTab, TabBase>
     {
     public:
-        SettingsTab(winrt::Microsoft::Terminal::Settings::Editor::MainPage settingsUI);
+        SettingsTab(winrt::Microsoft::Terminal::Settings::Editor::MainPage settingsUI,
+                    winrt::Windows::UI::Xaml::ElementTheme requestedTheme);
 
         void UpdateSettings(Microsoft::Terminal::Settings::Model::CascadiaSettings settings);
         void Focus(winrt::Windows::UI::Xaml::FocusState focusState) override;
 
         std::vector<Microsoft::Terminal::Settings::Model::ActionAndArgs> BuildStartupActions() const override;
 
     private:
+        winrt::Windows::UI::Xaml::ElementTheme _requestedTheme;
+
         void _MakeTabViewItem() override;
         winrt::fire_and_forget _CreateIcon();
+
+        virtual winrt::Windows::UI::Xaml::Media::Brush _BackgroundBrush() override;
     };
 }