add class for container div on 404 page

app/controllers/application_controller.rb

@@ -376,6 +376,7 @@ class ApplicationController < ActionController::Base
 
     def build_not_found_page(status=404, layout=false)
       category_topic_ids = Category.pluck(:topic_id).compact
+      @container_class = "container not-found-container"
       @top_viewed = Topic.where.not(id: category_topic_ids).top_viewed(10)
       @recent = Topic.where.not(id: category_topic_ids).recent(10)
       @slug =  params[:slug].class == String ? params[:slug] : ''

app/views/layouts/no_ember.html.erb

@@ -35,7 +35,7 @@
       </div>
     </div>
   </header>
-  <div id="main-outlet" class="container">
+  <div id="main-outlet" class="<%= @container_class ? @container_class : 'container' %>">
     <%= yield %>
   </div>
 </section>