genericise sidebar vertical offset css as it relates to the subnav

app/assets/stylesheets/framework/nav.scss

@@ -416,14 +416,16 @@
 
 .page-with-layout-nav {
   .right-sidebar {
-    top: ($header-height * 2) + 2;
+    top: ($header-height + 1) * 2;
   }
 
-  .build-sidebar {
-    top: ($header-height * 3) + 3;
+  &.page-with-sub-nav {
+    .right-sidebar {
+      top: ($header-height + 1) * 3;
 
-    &.affix {
-      top: 0;
+      &.affix {
+        top: 0;
+      }
     }
   }
 }

app/helpers/nav_helper.rb

@@ -31,7 +31,11 @@ module NavHelper
   end
 
   def layout_nav_class
-    "page-with-layout-nav" if defined?(nav) && nav
+    class_name = ''
+    class_name << " page-with-layout-nav" if defined?(nav) && nav
+    class_name << " page-with-sub-nav" if content_for?(:sub_nav)
+
+    class_name
   end
 
   def nav_control_class