I've added a box-shadow to the gnome-shell top panel
#panel {
...
box-shadow: 0px 2px 15px rgba(0,0,0,0.85);
z-index: -1;
}
The shadow is show but, as you can see from the image below, it covers maximized windows.
I tried adding a negative z-index attribute to panel style but it still covers the windows. Is there a way to have the windows layer above panel shadow?
I got in contact with GS developers and they clarified that this is a deliberate choice. The top panel is stacked above the windows group and that's why its shadow casts above them. This behavior won't change event in the future.