<Style TargetType="{x:Type local:ImGearMagnifierPopUpCtl} 
    <Setter Property="HorizontalAlignment" Value="Left"/>
    <Setter Property="VerticalAlignment" Value="Top"/>
        <Setter Property="Template 
          <Setter.Value>
            <ControlTemplate TargetType="{x:Type local:ImGearMagnifierPopUpCtl} 
              <Border 
                BorderBrush="#55000000" 
                CornerRadius="3" 
                BorderThickness="3" 
                Background="#55000000" 
                Width ="{Binding ParentCtl.PopupWidth}" 
                Height="{Binding ParentCtl.PopupHeight} 
                <Image Source="{Binding ParentCtl.MagnifiedImage}"/>
              </Border>
            </ControlTemplate>
          </Setter.Value>
        </Setter>
  </Style>