Can't use button property in trigger in WPF
===

I have button with custom content (a red circle) defined inside a user control and I want the circle to change to gray if the button is disabled.

I tried the following and it does not compile (Error: 'IsEnabled' member is not valid because it does not have a qualifying type name). Can any explain what I am doing wrong here?


    <Button>
        	<Button.Content>
                <Grid>
                     <Ellipse x:Name="circle" Width="20" Height="20" Fill="Red"/>
                </Grid>
             </Button.Content>
             <Button.Triggers>
                 <Trigger Property="IsEnabled" Value="False">
        		<Setter TargetName="circle" Property="Fill" Value="Gray"/>
                  </Trigger>
              </Button.Triggers>
        </Button>