Tweak header/footer css.

### Header

#### Before
![header-before](https://cloud.githubusercontent.com/assets/96776/5003003/9da51190-69bc-11e4-9475-1b67671b9590.png)

#### After
![header-after](https://cloud.githubusercontent.com/assets/96776/5003000/9d91bc3a-69bc-11e4-9e90-a1e575ed58e6.png)


### Footer

#### Before
![footer-before](https://cloud.githubusercontent.com/assets/96776/5003001/9d94f030-69bc-11e4-877e-e3b94c6a0ddc.png)
#### After
![footer-after](https://cloud.githubusercontent.com/assets/96776/5003002/9d962b8a-69bc-11e4-91cd-6c80749e87ef.png)