Semi-transparent custom layout panel

Question

I have built a semi-transparent custom layout panel in WPF by setting the Opacity value of the panel to 0.5. Everything works as expected, except that

Answer 1

Change the opacity of the brush, rather than control itself...

Answer 2

Thank you very much Anvaka, you helped me also. In my case, I did it from XAML (from style):

   <Setter Property="Background">
        <Setter.Value>
            <SolidColorBrush Color="Black" Opacity="0.3"/>
        </Setter.Value>
    </Setter>