Header Roe Filter symbol is not visible after applied custom style.

[Karthikeyan]

Hi,

After applied theme into the application, I'm changing RadGridView "GridViewHeaderCell and GridViewHeaderRow" as follows,

 <LinearGradientBrush x:Key="bs_Background" EndPoint="0.5,1" StartPoint="0.5,0">
            <GradientStop Color="#FFF21C1C" Offset="0.748" />
            <GradientStop Color="Black" Offset="0.198" />
        </LinearGradientBrush>

        <LinearGradientBrush x:Key="Brush_BackgroundGrad_Over" EndPoint="0.5,1" StartPoint="0.5,0">
            <GradientStop Color="Black" Offset="0.748" />
            <GradientStop Color="#FFF21C1C" Offset="0.198" />
        </LinearGradientBrush>
 <LinearGradientBrush x:Key="Brush_BackgroundGrad_Down" EndPoint="0.5,1" StartPoint="0.5,0">
            <GradientStop Color="#CCCC00" Offset="0.7"/>
            <GradientStop Color="#FFF21C1C" Offset="0.2"/>
        </LinearGradientBrush>

 <Style TargetType="telerik:GridViewHeaderRow">
         <Setter Property="Background" Value="{StaticResource bs_Background}" />
 </Style>

 <Style TargetType="telerik:GridViewHeaderCell">
            <Setter Property="Background" Value="{StaticResource bs_Background}" />
            <Setter Property="Foreground" Value="White"/>
            <Setter Property="BorderThickness" Value="0,1,1,1" />
            <Setter Property="VerticalContentAlignment" Value="Center" />
            <Setter Property="HorizontalContentAlignment" Value="Stretch" />
            <Setter Property="Padding" Value="5,0,3,0" />
            <Setter Property="Template">
                <Setter.Value>
                    <ControlTemplate TargetType="telerik:GridViewHeaderCell">
                        <Grid>
                            <VisualStateManager.VisualStateGroups>
                                <VisualStateGroup x:Name="CommonStates">
                                    <VisualStateGroup.Transitions>
                                        <VisualTransition GeneratedDuration="0:0:0.2"/>
                                    </VisualStateGroup.Transitions>
                                    <VisualState x:Name="MouseOver">
                                        <Storyboard>
                                            <DoubleAnimation Duration="0" To="1" Storyboard.TargetProperty="(UIElement.Opacity)"       Storyboard.TargetName="background_over" d:IsOptimized="True"/>
                                        </Storyboard>
                                    </VisualState>
                                    <VisualState x:Name="Normal"/>
                                </VisualStateGroup>
                            </VisualStateManager.VisualStateGroups>
                            <Rectangle x:Name="background" Margin="1" Fill="{StaticResource bs_Background}"/>
                            <Rectangle x:Name="background_over" Margin="2" Opacity="0" Fill="{StaticResource Brush_BackgroundGrad_Over}"/>
                            <Rectangle x:Name="background_down" Margin="2" Opacity="0" Fill="{StaticResource Brush_BackgroundGrad_Down}"/>
                            <ContentPresenter x:Name="contentPresenter" HorizontalAlignment="Center" VerticalAlignment="Center" Margin="3"/>
                        </Grid>
                    </ControlTemplate>
                </Setter.Value>
            </Setter>

        </Style>

After applied as mentioned above, I cannot see the filter symbol in the gridcell.
Please guide how to get that filter symbol.

Thanks in advance,
Karthikeyan Manickam.