Basic CSS gradient fix for choices

The “top” on the other styles (-moz-linear-gradient,
-webkit-linear-gradient, etc) signifies “start at the top”.  The
equivalent basic “linear-gradient” style is “to bottom”, not “to top”.

Before commit:
![image](https://cloud.githubusercontent.com/assets/3732514/3767483/cb6592fc-18cd-11e4-97c9-2095b081c268.png)

After commit:
![image](https://cloud.githubusercontent.com/assets/3732514/3767499/e6c57990-18cd-11e4-85fb-679c525e4892.png)