Brings tabs closer to 8shapes recommendations

+ Lightens the detail header background
+ Inverts the color of header text
+ Shrinks the border between the tab header and content

Before:
![tabs_before](https://cloud.githubusercontent.com/assets/186715/4728934/f839b4da-597c-11e4-8bd1-bf7f464da59d.png)

After:
![screen shot 2014-10-21 at 7 23 33 pm](https://cloud.githubusercontent.com/assets/186715/4730025/735a08f8-5992-11e4-9068-4d8f018e7405.png)