Update template.css

Following the tracker : http://joomlacode.org/gf/project/joomla/tracker/?action=TrackerItemEdit&tracker_item_id=31370 

This is not an error/bug but just a proposal to improve the Protostar contact form to make it "responsive".
Also, as this is my first pull request, thanks to tell me if I've made mistakes ...
Front-end with Protostar template, (sample data installed)
For example :
FE -> All Front End Views -> Single Contact -> Contact Form
The fields do not seem to be responsive, the display on mobile media is not optimum.
This PR aims to make this form responsive, perhaps I miss things but thank you to test and make your remarks.