Improve repository file syntax highlighting

The default syntax highlighting isn't the best. Without a ton of work, we can add some CSS to override default syntax highlighting.

Using DevTools, I tested this out and have included some sample screenshots of a dark theme that I found and tweaked a bit. This could be implemented by simply adding some CSS to the Pepper theme.

![screen shot 2014-01-09 at 2 45 55 pm](https://f.cloud.github.com/assets/1437322/1882605/570223b6-7978-11e3-9196-226a92990b15.png)

![screen shot 2014-01-09 at 2 46 29 pm](https://f.cloud.github.com/assets/1437322/1882609/6a4f03a8-7978-11e3-9636-9d7d50f02b4f.png)

![screen shot 2014-01-09 at 2 47 21 pm](https://f.cloud.github.com/assets/1437322/1882613/77ef0760-7978-11e3-9b65-910ae5b4f047.png)