Fixed default-shadow mixin

app/assets/stylesheets/_settings.scss

@@ -22,6 +22,8 @@ $colour-5: #8EA604;
 		}
 		@if $additional-shadow {
 			$additional-shadow: ', #{$additional-shadow}';
+		} @else {
+			$additional-shadow: '';
 		}
 		@include _(box-shadow, #{$offset} 0.8em #{-0.2em * $distance} #000#{$additional-shadow});
 	}