Tweak splash example controls style

The splash example controls seems to breaks on Chrome v40+. Currently, it switches `justify-content` property by using media queries, but I don't feel to need it because it can be maintained looks without that switching. This issue resolves by this change.

I confirmed it works on following browsers.

* Chrome v39 (stable)
* Chrome v40 (beta)
* Chrome v41 (canary)
* Firefox v34 (stable)
* Firefox v36 (Developer Edition)
* Safari v8 (OS X Yosemite)
* Safari v8 (iOS on iPhone 5s)
* Opera v26 (stable)

![2014-12-13 at 18 57](https://cloud.githubusercontent.com/assets/34588/5423325/10273f58-82fa-11e4-88f0-282bc10082fd.png)