Some improvements to the Twilight theme.

Sample screenshots:

![example 1](https://cloud.githubusercontent.com/assets/1465469/3677446/a21530de-1291-11e4-9f47-3b056543be06.png)

![example 2](https://cloud.githubusercontent.com/assets/1465469/3677447/a215d430-1291-11e4-9676-c0a52d6d45f8.png)