This is due to the borderless windows in unity, you can change this by changing -UnityDecoration-extents in /usr/share/themes/Ambiance/gtk-3.0/apps/unity.css
This is due to the borderless windows in unity, you can change this by changing -UnityDecoratio n-extents in /usr/share/ themes/ Ambiance/ gtk-3.0/ apps/unity. css