How to make expander button clickable?

Question

WPF

I make a button in the expander like this:

<Expander x:Name="expander" Header="Настройки">
  <StackPanel Height="200" VerticalAlignment="Top" Background="#FFB9DEB8" >
    <Button x:Name="extended"  Click="extended_Click" Width="200" Height="30" IsHitTestVisible="True" HorizontalContentAlignment="Center" VerticalContentAlignment="Center" HorizontalAlignment="Left" VerticalAlignment="Top" Content="Включить расширенный режим"/>
  </StackPanel>
</Expander>

compile run - the button is not pressed!
tell me what am I doing wrong?