If you love Arc Dark, you'll love Linux Mint's Mint-Y series of themes. Wrote a guide about it here.
Might remodel that guide since the URLs had changed since, just grab packages for latest Linux Mint and install it. No time for redos as of present. What you get in return are a bunch of Greybird and Arc derivatives with varying colours so you can have a rotating selection of Arc-alikes with corresponding icon suites. Did it.