Button Flyout has a border I can't remove - xaml

Question

I have a button with a flyout and for some reason I can't remove the border, white, around the black grid. Any suggestions?
Picture of output
Xaml Implementation
<Button Foreground="Transparent" HorizontalAlignment="Right" Width="30" Height="30" Margin="0,0,15,5">
<Button.Background>
<ImageBrush ImageSource="ms-appx:///Assets/ButtonImage.png" />
</Button.Background>
<Button.Flyout>
<Flyout Placement="Top" >
<Grid Width="300" Height="auto" Margin="0,0,0,0" Background="Black" BorderThickness="3" BorderBrush="blue" >
<Grid.RowDefinitions>
<RowDefinition Height="*" />
<RowDefinition Height="*" />
<RowDefinition Height="*" />
<RowDefinition Height="*" />
</Grid.RowDefinitions>
<Grid Height="50" Grid.Row="0" Background="Black" BorderBrush="Black">
<TextBlock x:Name="SSMenuAppVersionText" Text="123" FontSize="15" HorizontalAlignment="Center" VerticalAlignment="Center" />
</Grid>
<Grid x:Name="AppSuggestionGrid" Grid.Row="1" Background="Black" BorderBrush="Black">
<Button x:Name="AppSuggestionButton" Click="FeedBackButtonClicked" Background="Transparent" Height="50" HorizontalAlignment="Stretch">
<TextBlock x:Name="SSMenuAppSuggesstionText" Text="App Suggestions" Foreground="#007AFF" FontSize="14" HorizontalAlignment="Center" VerticalAlignment="Center" />
</Button>
</Grid>
<Grid Grid.Row="2" BorderBrush="Black" Background="Black">
<Button x:Name="ReferButton" Click="ReferButtonClicked" Background="Black" Height="50" HorizontalAlignment="Stretch">
<TextBlock x:Name="SSMenuReferText" Text="Refer " Foreground="#007AFF" FontSize="14" HorizontalAlignment="Center" VerticalAlignment="Center" />
</Button>
</Grid>
<Grid Grid.Row="3" BorderBrush="Black" Background="Black">
<Button x:Name="VisitButton" Click="VisitButtonClicked" Background="Black" Height="50" HorizontalAlignment="Stretch">
<TextBlock x:Name="SSMenuVisitText" Text="Visit " Foreground="#007AFF" FontSize="14" HorizontalAlignment="Center" VerticalAlignment="Center" />
</Button>
</Grid>
</Grid>
</Flyout>
</Button.Flyout>
</Button>

Answer 1

You have options. If we go look at the guts of the Flyout Style Template we notice some set theme resources for Padding and Border which you can use to either override the properties, or just create your own Style template for Flyout and make them whatever you like.
So for example if you went and tossed something like this into your resource dictionary, you should override the ThemeResource for the app.
<Thickness x:Key="FlyoutContentThemePadding">0,0,0,0</Thickness>
<Thickness x:Key="FlyoutBorderThemeThickness">0</Thickness>
Hope this helps, cheers!