ia.css: remove dropshadow in the collapsed dropdown.

Before:
![screen shot 2014-12-15 at 12 01 46 pm](https://cloud.githubusercontent.com/assets/81969/5439959/2f1d9e76-8452-11e4-9edf-dfc54cf66bec.png)


After:
![screen shot 2014-12-15 at 12 01 28 pm](https://cloud.githubusercontent.com/assets/81969/5439960/32cbb94a-8452-11e4-8510-a65b5a096f77.png)