Give config a dedicated background-color

Most of the rest of the settings view defines it's own color scheme, but hover on the config menu items reverts to the ui theme's colors. This fixes that.

**Before**
![image](https://f.cloud.github.com/assets/136521/2323886/515219f2-a3c2-11e3-89b0-1f1d44d2b3ae.png)

**After**
![image](https://f.cloud.github.com/assets/136521/2323879/3f08dfec-a3c2-11e3-9908-351301cab966.png)


cc @kevinsawicki