OnlineMonitorSystem/HandyControl/HandyControl_Shared/Themes/Styles/Base/MagnifierBaseStyle.xaml

<ResourceDictionary xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
                    xmlns:hc="clr-namespace:HandyControl.Controls">

    <Style x:Key="MagnifierBaseStyle" TargetType="hc:Magnifier">
        <Setter Property="IsHitTestVisible" Value="False" />
        <Setter Property="HorizontalAlignment" Value="Left"/>
        <Setter Property="VerticalAlignment" Value="Top"/>
        <Setter Property="Width" Value="180"/>
        <Setter Property="Height" Value="180"/>
        <Setter Property="BorderThickness" Value="8"/>
        <Setter Property="Background" Value="{DynamicResource BackgroundBrush}"/>
        <Setter Property="BorderBrush" Value="{DynamicResource BorderBrush}"/>
        <Setter Property="Template">
            <Setter.Value>
                <ControlTemplate TargetType="hc:Magnifier">
                    <Border Style="{StaticResource BorderCircular}" BorderBrush="{TemplateBinding BorderBrush}" BorderThickness="{TemplateBinding BorderThickness}" Background="{TemplateBinding Background}">
                        <Ellipse>
                            <Ellipse.Fill>
                                <VisualBrush Visual="{Binding Target,RelativeSource={RelativeSource TemplatedParent}}" ViewboxUnits="Absolute" x:Name="PART_VisualBrush"/>
                            </Ellipse.Fill>
                        </Ellipse>
                    </Border>
                </ControlTemplate>
            </Setter.Value>
        </Setter>
    </Style>

</ResourceDictionary>