extend assets path with jquery-ui images, so rails can find them

config/application.rb

@@ -44,5 +44,8 @@ module Gitlab
 
     # Version of your assets, change this if you want to expire all your assets
     config.assets.version = '1.0'
+
+    # Extend assets path
+    config.assets.paths << Rails.root.join('vendor', 'assets', 'images', 'jquery-ui')
   end
 end