Transparent nav-list items

It was happening because `fc-item` comes with a background colour by default (probably for the best).

Before:
![screen shot 2014-10-23 at 15 09 32](https://cloud.githubusercontent.com/assets/1607666/4754485/4fc2959a-5abe-11e4-8cd6-fc6a6bb7de48.png)

After:
![screen shot 2014-10-23 at 15 09 57](https://cloud.githubusercontent.com/assets/1607666/4754486/4fd4aa14-5abe-11e4-97f3-b4d4d66fe5f3.png)