When color theme is used, ContentDialog covers the whole page

[under3415]

Steps to replicate:

1. Create new UWP app
2. Grab a color scheme from Fluent XAML Theme Editor and add it to your project
3. In App.Xaml add this:

    <Application.Resources>
     <ResourceDictionary>
      <ResourceDictionary.MergedDictionaries>
          <ResourceDictionary Source="Dictionary1.xaml"/>
     </ResourceDictionary.MergedDictionaries>
    </ResourceDictionary>
   </Application.Resources>

4. Add a TextBlock and Loaded event to MainPage

5. Add ContentDialog call to Loaded event

   private async void Page_Loaded(object sender, Windows.UI.Xaml.RoutedEventArgs e)
       {
           ContentDialog noWifiDialog = new ContentDialog
           {
               Title = "No wifi connection",
               Content = "Check your connection and try again.",
               CloseButtonText = "Ok"
           };
   
           _ = await noWifiDialog.ShowAsync();
       }

6. Run the app and see how ContentDialog covers up the TextBlock. If you remove the color theme this does not happen.

[under3415]

You need to add this to your theme to fix the ContentDialog issue

      <SolidColorBrush x:Key="SystemControlPageBackgroundMediumAltMediumBrush" Color="#99000000" />
                            <StaticResource x:Key="ContentDialogLightDismissOverlayBackground" ResourceKey="SystemControlPageBackgroundMediumAltMediumBrush" />