WPF

<Window x:Class="TestingPOS.Window1"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:local="clr-namespace:TestingPOS.Controls"
        x:Name="MainWindow"
        
    Title="Window1" Height="600" Width="600" Background="Transparent" AllowsTransparency="True" WindowStyle="None" MouseLeftButtonDown="Window_MouseLeftButtonDown">
    
    <Window.Template>
        <ControlTemplate>
            <Rectangle Stroke="Black" RadiusX="97.5" RadiusY="97.5" Canvas.Top="36">
                <Rectangle.Fill>
                    <LinearGradientBrush EndPoint="0.5,1" StartPoint="0.5,0">
                        <GradientStop Color="Black" Offset="0"/>
                        <GradientStop Color="White" Offset="1"/>
                    </LinearGradientBrush>
                </Rectangle.Fill>
            </Rectangle>
        </ControlTemplate>
    </Window.Template>
   
    
</Window>

private BitmapImage ConvertIconToBitmapImage(Icon icon)
{
    Bitmap bitmap = icon.ToBitmap();

    MemoryStream ms = new MemoryStream();
    bitmap.Save(ms, System.Drawing.Imaging.ImageFormat.Jpeg);
    BitmapImage bImg = new BitmapImage();

    bImg.BeginInit();
    bImg.StreamSource = new MemoryStream(ms.ToArray());
    bImg.CreateOptions = BitmapCreateOptions.None;
    bImg.CacheOption = BitmapCacheOption.Default;
    bImg.EndInit();

    ms.Close();

    return bImg;
}