Private/Window.xaml

<Window xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
Width="320" Height="180"
AllowsTransparency="True"
Background="Transparent"
WindowStyle="None">
    <Grid>
    </Grid>
    <Window.TaskbarItemInfo>
         <TaskbarItemInfo>
          <TaskbarItemInfo.ThumbButtonInfos>
            <ThumbButtonInfoCollection/>
          </TaskbarItemInfo.ThumbButtonInfos>
         </TaskbarItemInfo>
    </Window.TaskbarItemInfo>
    <Window.Resources>
        <DataTemplate x:Key="OverlayBadge">
            <Grid Width="{Binding BadgeSize}" Height="{Binding BadgeSize}">
                <Rectangle Fill="{Binding BackgroundColor}"
                            Stroke="{Binding ForegroundColor}"
                            StrokeThickness="{Binding FrameWidth}"
                            RadiusX="{Binding Radius}"
                            RadiusY="{Binding Radius}"/>
     
                <TextBlock Text="{Binding Text}"
                            TextAlignment="Center"
                            VerticalAlignment="Center"
                            Foreground="{Binding ForegroundColor}"
                            FontWeight="Bold"
                            FontSize="{Binding FontSize}" />
            </Grid>
        </DataTemplate>
    </Window.Resources>
</Window>