Adding CSS for nav dropdown arrow A/B test

Will allow for A/B test which will create the following variant:

![screen shot 2014-12-05 at 14 31 09](https://cloud.githubusercontent.com/assets/883598/5317491/59206458-7c8f-11e4-8932-c61688c74a1a.png)
![screen shot 2014-12-05 at 14 31 28](https://cloud.githubusercontent.com/assets/883598/5317490/59207ccc-7c8f-11e4-936f-fffb68b7aa46.png)