CSS for sidebar should go the length of the page

Note the gray section in the sidebar / side-nav only goes the length of the content:

![screen_shot_013](https://cloud.githubusercontent.com/assets/520669/9016161/a1c4ce7e-3783-11e5-9b62-7c5ae820b17d.png)
