CUSTOMIZE button top up site

I hope someone can give me a hand, I can not find the way to change the color to the button to upload up that inserts generate press in the bottom of the site, in the footer area, I have gone crazy and I can not find any type of orientation, please someone knows how to change the color of this button to be able to assign a color according to the colors of the site? from already a thousand thanks

The page I need help with: [log in to see the link]