Not able to set GridViewToggleButton style

[Pravin]

Hi,
I would like to change the +/- symbol on a GridViewToggleRowDetailsColumn so i have created below ControlTemplate

<ControlTemplate x:Key="GridViewToggleButtonTemplate" TargetType="telerik:GridViewToggleButton">

                   <Border Background="Transparent" VerticalAlignment="Stretch" HorizontalAlignment="Stretch">

                       <Border Width="80" Height="20"

                   Background="{TemplateBinding Background}"

                   BorderBrush="{TemplateBinding BorderBrush}"               

                   BorderThickness="{TemplateBinding BorderThickness}"

                   VerticalAlignment="{TemplateBinding VerticalContentAlignment}"

                   HorizontalAlignment="{TemplateBinding HorizontalContentAlignment}">

                           <Grid x:Name="myGrid">

                               <TextBlock Text="Details" HorizontalAlignment="Center" VerticalAlignment="Center"/>

                           </Grid>

                       </Border>

                   </Border>

                   <ControlTemplate.Triggers>

                       <Trigger Property="IsChecked" Value="True">

                           <Setter TargetName="myGrid" Property="Background" Value="Red" />

                       </Trigger>

                   </ControlTemplate.Triggers>

  

               </ControlTemplate>

  

               <Style TargetType="telerik:GridViewToggleButton" x:Key="toggleButtonStyle">

                   <Setter Property="Template" Value="{StaticResource GridViewToggleButtonTemplate}" />

               </Style>

And applied this style in telerik:RadGridView.Columns as below

<telerik:GridViewToggleRowDetailsColumn ToggleButtonStyle="{StaticResource toggleButtonStyle}" />

But this doesn't work so please let know how do i fix this problem.
Thanks in advance.