Change event details page background colour to e7edf0.

Resolves ticket #882367 (https://bugzilla.mozilla.org/show_bug.cgi?id=882367).

assets/css/event_details.less

@@ -1,5 +1,5 @@
 body#events.details {
-    background: #3fb58e;
+    background: #e7edf0;
 
     #details-pane {