use the background from the control when we can

src/cascadia/TerminalApp/AdminWarningPlaceholder.cpp

@@ -15,6 +15,13 @@ namespace winrt::TerminalApp::implementation
         _Commandline{ cmdline }
     {
         InitializeComponent();
+        // If the content we're hosting is a TermControl, then use the control's
+        // BG as our BG, to give the impression that it's there, under the
+        // dialog.
+        if (const auto termControl{ control.try_as<winrt::Microsoft::Terminal::Control::TermControl>() })
+        {
+            RootGrid().Background(termControl.BackgroundBrush());
+        }
     }
     void AdminWarningPlaceholder::_primaryButtonClick(winrt::Windows::Foundation::IInspectable const& /*sender*/,
                                                       RoutedEventArgs const& e)

src/cascadia/TerminalApp/AdminWarningPlaceholder.xaml

@@ -11,6 +11,18 @@
              xmlns:mux="using:Microsoft.UI.Xaml.Controls"
              mc:Ignorable="d">
 
+    <!--
+        We have to use two grids to be tricky here:
+        - The outer grid will get its background from the control it hosts, and
+        expands to fit its container. This will make it look like the background
+        fills the space available.
+        - The inner grid is set to Center,Center, so that the "dialog" appears
+        centered
+    -->
+
+    <Grid x:Name="RootGrid"
+          HorizontalAlignment="Stretch"
+          VerticalAlignment="Stretch">
         <Grid HorizontalAlignment="Center"
               VerticalAlignment="Center">
             <Border Margin="8,8,8,8"
@@ -56,5 +68,6 @@
                 </StackPanel>
             </Border>
         </Grid>
+    </Grid>
 
 </UserControl>

src/cascadia/TerminalApp/TerminalPage.cpp

@@ -1597,10 +1597,9 @@ namespace winrt::TerminalApp::implementation
     // - true if we should prompt the user for approval.
     bool TerminalPage::_shouldPromptForCommandline(const winrt::hstring& cmdline) const
     {
-        // NOTE: For debugging purposes, changing this to `true ||
-        // _isElevated()` is a handy way of forcing the elevation logic, even
-        // when unelevated.
-        if (_isElevated())
+        // NOTE: For debugging purposes, changing this to `true || _isElevated()`
+        // is a handy way of forcing the elevation logic, even when unelevated.
+        if (true || _isElevated())
         {
             // If the cmdline is EXACTLY an executable in
             // `C:\WINDOWS\System32`, then ignore this check.

src/cascadia/TerminalControl/TermControl.cpp

@@ -2590,4 +2590,9 @@ namespace winrt::Microsoft::Terminal::Control::implementation
     {
         return _core.ReadEntireBuffer();
     }
+
+    Media::Brush TermControl::BackgroundBrush()
+    {
+        return RootGrid().Background();
+    }
 }

src/cascadia/TerminalControl/TermControl.h

@@ -111,6 +111,8 @@ namespace winrt::Microsoft::Terminal::Control::implementation
 
         hstring ReadEntireBuffer() const;
 
+        Windows::UI::Xaml::Media::Brush BackgroundBrush();
+
         // -------------------------------- WinRT Events ---------------------------------
         // clang-format off
         WINRT_CALLBACK(FontSizeChanged, Control::FontSizeChangedEventArgs);

src/cascadia/TerminalControl/TermControl.idl

@@ -71,5 +71,7 @@ namespace Microsoft.Terminal.Control
         void ToggleReadOnly();
 
         String ReadEntireBuffer();
+
+        Windows.UI.Xaml.Media.Brush BackgroundBrush { get; };
     }
 }

src/cascadia/TerminalSettingsModel/WslDistroGenerator.cpp

@@ -42,7 +42,7 @@ static winrt::com_ptr<implementation::Profile> makeProfile(const std::wstring& d
     wil::unique_cotaskmem_string systemPath;
     THROW_IF_FAILED(wil::GetSystemDirectoryW(systemPath));
     std::wstring command(systemPath.get());
-    WSLDistro->Commandline(command + L"\\wsl.exe -d " + distName);
+    WSLDistro->Commandline(winrt::hstring{ command + L"\\wsl.exe -d " + distName });
     WSLDistro->DefaultAppearance().ColorSchemeName(L"Campbell");
     WSLDistro->StartingDirectory(winrt::hstring{ DEFAULT_STARTING_DIRECTORY });
     WSLDistro->Icon(L"ms-appx:///ProfileIcons/{9acb9455-ca41-5af7-950f-6bca1bc9722f}.png");