Toggle background opaque box on mobile
## **OLD issue description**

This is a regression after 2.0.1 so we need to sort it out.

https://github.com/twbs/ratchet/pull/478/files#diff-c1b9f363394d82a27c793f86d9888be9L254

I feel like Sass 3.3 is more trouble than worth yet. The only real gain is the ability to be able to use `@at-root`...

/CC @connors 
