studio - alerts: hiding alerts (in possbily inaccessible ways) in css for page load's sake

cms/static/sass/elements/_alerts.scss

@@ -453,6 +453,14 @@
   padding: $baseline ($baseline*2) ($baseline*1.5) ($baseline*2);
   background: $gray-d3;
 
+  // needed since page load is very slow
+  display: none;
+
+  // needed since page load is very slow
+  &.is-shown {
+    display: block;
+  }
+
   &.wrapper-alert-warning {
     @include box-shadow(0 1px 1px $white, inset 0 2px 2px $shadow-d1, inset 0 -4px 1px $orange);