Created attachment 254053 [details]
Screenshot of the difference between CSD and non-CSD shadows

The shadows for CSD windows appear much thicker and heavier than the shadows for non CSD windows. I'm attaching a screenshot that shows both side by side in which you can easily see the difference.
The CSD shadow also has a rather sharp edge which somewhat destroys the illusion of it being a shadow.
Setting wm_shadow to alpha(black, 0.5) or alpha(black, 0.4) makes the shadows look much more similar in terms of intensity.
There are probably additional adjustments that could be made to fix the sharp edge but I guess that would require either changing the gtk blur/shadow algorithm (if that it is even possible and not defined by the css standard) or adjusting the blur etc. values but before you can increase that https://bugzilla.gnome.org/show_bug.cgi?id=705343 needs to be fixed first.