After applying this setting in Compiz our menu and panel (although not noticeable in the screenshot) will look like this
Let’s see like this
What we need to do is open the Compiz Config Options Manager (We already saw how to install here) which is in System-> Preferences and we look for the option Opacity Brigthness and Saturation
once inside we will see something like the screenshot that follows, inside the section windows specific settings we enter a new line (clicking on new) and a window will open in which we will enter the next one.
(Name = gnome-panel) | (Type = Menu | PopupMenu | DropdownMenu | Dialog | ModalDialog)
en windows value land we give the value of transparency that we like best 85 is in my case.
Another tip, if you want the windows to be transparent when you move the icon move Window
and bring the opacity section to the level of transparency you like.