I just installed Arc theme on Ubuntu 16.04 using version for ubuntu 15.10 (that's what's available on creator's website: http://software.opensuse.org/download.html?project=home%3AHorst3180&package=arc-theme)
Here's how it looks on my setup:
I activated this theme using Unity Tweak Tool.
Firstly in Nautilus the left panel looks weird - it should also be transparent. Secondly every window gets a little thicker just below titlebar on both sides.
Do you know if there's a way to fix it? I really like this theme, probably best available.