To center the Extra Theme footer links (a.k.a. the copyright notice), you can use the following CSS:

#footer-info { width: 100%; margin:0 auto; text-align: center !important; }
@media only screen and (min-width: 769px) { 
	#footer-nav { margin-top:-26px !important; } 

It applies a standard centering of the footer links, and on wide screens also moves the footer links up slightly to compensate for the presence of the social media icons which would otherwise push it down.