I've done this last week but haven't posted here. A CSS mod via chrome extension called stylebot. When you add the extension, you'll be able to apply any mod submitted for a given site from its menu. "Install style from social"

Black NiceHash:
http://stylebot.me/styles/5879

Screenshot is old but code is updated to work with new site updates. Font is also changed because it wasn't very comfortable on chrome.

This just changes the css but if you're skeptical, wait for a probable NiceHash approval.
Enjoy.