Board Thread:Support Requests - Getting Technical/@comment-4370375-20160804013336/@comment-29138396-20160806181755

Echoblast53 wrote: Uh... yes you can, but I foresee defining how each gradient would look like: It's supported by most of the popular browsers (exclude IE and Edge). While building this, I was assuming colors came in pairs, dark came first on the left, and the gradient was left to right. Is this what you are looking for? (Example) Neat, I didn't know CSS variables existed.

The page you linked though shows that it doesn't support Edge which is a browser Wikia actively seeks to support so for now you should probably hold off on using them.