Example of a popup control in Xaml with nice triangle

Popup.xaml

   <Grid x:Name="LayoutRoot" Background="Transparent" Margin="0,55,0,0">
        <Grid Background="White" Margin="0,10,0,0">
            <Grid.RowDefinitions>
                <RowDefinition Height="Auto" />
                <RowDefinition Height="*" />
            </Grid.RowDefinitions>
            <StackPanel Grid.Row="0" Margin="20" Background="Transparent">
                <TextBlock Text="Listening" FontSize="36" Margin="0"/>
            </StackPanel>
            <StackPanel Grid.Row="1" Margin="20" Background="Transparent" VerticalAlignment="Bottom">
                <TextBlock Text="Home" FontSize="36" Margin="0,0,0,10"/>
                <TextBlock Text="Profile" FontSize="36" Margin="0,0,0,10"/>
                <TextBlock Text="Setting" FontSize="36" Margin="0,0,0,10"/>
            </StackPanel>
        </Grid>
        <Polygon
              Points="0,0 2,0 1,-1" Fill="White"
              Width="20" Height="10" Margin="0,0,25,0"
              Stretch="Fill" HorizontalAlignment="Right" VerticalAlignment="Top" />
    </Grid>