Change "NEW" marker to use W3C blue background (#4145)

Instead of the original red - see
#1481 (comment)

(cherry picked from commit 104b82b)

Author: patrickhlauke

guidelines/guidelines.css

@@ -5,7 +5,7 @@
 .change {
     display: inline;
     color: #fff;
-    background: #B50000;
+    background: #005A9C;
     border-radius: 0.25em;
     padding: 0.25em 0.4em;
     margin: 0 0.25em 0 0;