fixed mixin sass

common/static/sass/_mixins.scss

@@ -268,7 +268,7 @@
 .ui-loading {
   @include animation(fadeIn $tmg-f2 linear 1);
   @extend %ui-well;
-  @extend %t-base-copy;
+  @extend %t-copy-base;
   opacity: .6;
   background-color: $white;
   padding: ($baseline*1.5) $baseline;