I know there is a Notebook option
WindowOpacity can be used to adjust the opacity of a whole notebook. But what I want is keeping the text and graphics and so on being
Opacity while the other parts of the window being
Opacity[0.3], which may look like (the pic is roughly produced by photoshop):
I guess this effect might be achieved by capture the screen prior and set it as the background of a Cell/Cells. But even if that is applicable, it must be very inefficiency.
My questions are: how to achieve this transparent effect in Mathematica (maybe with some help from external applications)? and how to do it effectively?