Wpf button in groupbox checked style

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WPF

groupbox

Hi,

I wan to change the background color of a button in a groupBox when it's selected.
I don't find the trigger for this.

<Style x:Key="MyButton" TargetType="Button">
 <Setter Property="OverridesDefaultStyle" Value="True" />
 <Setter Property="Cursor" Value="Hand" />
 <Setter Property="Template">
  <Setter.Value>
    <ControlTemplate TargetType="Button">
     <Border Name="border" CornerRadius="5" Height="48" Width="48 Background="#424242" BorderThickness="0">
     <ContentPresenter HorizontalAlignment="Center" VerticalAlignment="Center" />
       </Border>
         <ControlTemplate.Triggers>
           <Trigger Property="IsMouseOver" Value="True">
             <Setter Property="Opacity" Value="0.8" />
                </Trigger>
                   <Trigger Property="ToggleButton.IsPressed" Value="True">
                      <Setter TargetName="border" Property="Background" Value="Orange" />
                </Trigger>
                </ControlTemplate.Triggers>
                </ControlTemplate>
            </Setter.Value>
        </Setter>
    </Style>

What I have tried:

Toggle.Pressed for example is changing the background for a second

<Trigger Property="ToggleButton.IsPressed" Value="True">
 <Setter TargetName="border" Property="Background" Value="Orange" />
</Trigger>