Describe the bug
In recent versions of WinUI, MenuFlyouts have a gray background in high contrast themes. They should have the page background color.

Steps to reproduce the bug
Add the following XAML to a test app:

<Button Content="Open Flyout">
  <Button.Flyout>
    <MenuFlyout>
      <MenuFlyoutItem Text="Test 1"></MenuFlyoutItem>
      <MenuFlyoutItem Text="Test 2"></MenuFlyoutItem>
    </MenuFlyout>
  </Button.Flyout>
</Button>

Expected behavior
The background of a MenuFlyout should match the user's preferred background color, like it does in Windows.UI.Xaml.

Screenshots

Version Info

NuGet package version:
Microsoft.UI.Xaml 2.3.200213001
Microsoft.UI.Xaml 2.4.0

Additional context
Internal bug: 26080077.