Improved selected styles

The current `.selected` styles made the script unreadable, this PR improves that.

### From
![JSONSelect - from](https://f.cloud.github.com/assets/749025/198747/db0c235e-8064-11e2-8fac-2a176cd76194.png)

### To
![JSONSelect - to](https://f.cloud.github.com/assets/749025/198749/df25e830-8064-11e2-8aa4-2fb533dfb203.png)