modified popup css to match native styles

Issue
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Popup styles was not matching native design

Test case
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Check popup for different os theme in kitchen sink app

![photo nov 18 5 38 25 pm](https://f.cloud.github.com/assets/1414842/1569097/7a96ab14-50bd-11e3-80c6-1a8e6a6cf4a2.png)


Fix
-
modified css to match native design

![untitled](https://f.cloud.github.com/assets/1414842/1569093/6f9c12da-50bd-11e3-9220-6ae344cba7f7.png)