diff -r 4169862209f5 app/controllers/application_controller.rb
--- a/app/controllers/application_controller.rb	Sun Jan 19 02:44:29 2020 +0000
+++ b/app/controllers/application_controller.rb	Tue Jan 21 07:36:44 2020 +0100
@@ -529,6 +529,12 @@
     request.xhr? ? false : 'base'
   end
 
+  #adds css class to body tag of layout
+  def add_body_css_class(css_class)
+    @css ||= []
+    @css << css_class
+  end
+
   def render_feed(items, options={})
     @items = (items || []).to_a
     @items.sort! {|x,y| y.event_datetime <=> x.event_datetime }
diff -r 4169862209f5 app/helpers/application_helper.rb
--- a/app/helpers/application_helper.rb	Sun Jan 19 02:44:29 2020 +0000
+++ b/app/helpers/application_helper.rb	Tue Jan 21 07:36:44 2020 +0100
@@ -637,20 +637,20 @@
   # Returns the theme, controller name, and action as css classes for the
   # HTML body.
   def body_css_classes
-    css = []
+    @css ||= []
     if theme = Redmine::Themes.theme(Setting.ui_theme)
-      css << 'theme-' + theme.name
+      @css << 'theme-' + theme.name
     end
 
-    css << 'project-' + @project.identifier if @project && @project.identifier.present?
-    css << 'has-main-menu' if display_main_menu?(@project)
-    css << 'controller-' + controller_name
-    css << 'action-' + action_name
-    css << 'avatars-' + (Setting.gravatar_enabled? ? 'on' : 'off')
+    @css << 'project-' + @project.identifier if @project && @project.identifier.present?
+    @css << 'has-main-menu' if display_main_menu?(@project)
+    @css << 'controller-' + controller_name
+    @css << 'action-' + action_name
+    @css << 'avatars-' + (Setting.gravatar_enabled? ? 'on' : 'off')
     if UserPreference::TEXTAREA_FONT_OPTIONS.include?(User.current.pref.textarea_font)
-      css << "textarea-#{User.current.pref.textarea_font}"
+      @css << "textarea-#{User.current.pref.textarea_font}"
     end
-    css.join(' ')
+    @css.join(' ')
   end
 
   def accesskey(s)