Modified css to make zoom buttons a little easier to see.

Made a few minor changes to the css file to make the zoom buttons a little easier to see. See attached image to compare modified style with original style. The new style is displayed on the left side.

![capture](https://cloud.githubusercontent.com/assets/134743/4929761/15929916-6558-11e4-978d-78704d9c70e5.JPG)