Improve design of nav list container

Before:
![screen shot 2014-10-24 at 12 32 23](https://cloud.githubusercontent.com/assets/813383/4768902/cf5f2030-5b71-11e4-8ff4-0ef5acf546e0.png)

After:
![screen shot 2014-10-24 at 12 33 11](https://cloud.githubusercontent.com/assets/813383/4768904/d398c2dc-5b71-11e4-95ec-45975ad4f3ef.png)