It seems that Pantheon applications mess with i3 by adding a huge gap between windows/frames like in the screenshot below.
Is there a way to use Pantheon applications in i3 without that border/margin? I guess it's the shadows of Pantheon applications that cause this, so is there a way to disable them?
(I'm running Elementary OS 0.4 x86_64 with i3 v4.11. My previous desktop manager was lightdm v1.18.3, which is still installed.)