Index: wp-content/themes/twentytwelve/style.css
===================================================================
--- wp-content/themes/twentytwelve/style.css	(revision 22125)
+++ wp-content/themes/twentytwelve/style.css	(working copy)
@@ -1593,11 +1593,6 @@
 		box-shadow: none;
 	}
 	.site-content {
-		float: left;
-		margin: 0;
-		width: 100%;
-	}
-	.site-content {
 		margin: 0;
 		width: auto;
 	}