Compensate for scrollbar disappearing when media modal visible (#8100)

* Compensate for scrollbar disappearing when media modal visible

Make auth pages backgrounds lighter

* Fix typo

app/controllers/auth/sessions_controller.rb

@@ -9,6 +9,7 @@ class Auth::SessionsController < Devise::SessionsController
   skip_before_action :check_suspension, only: [:destroy]
   prepend_before_action :authenticate_with_two_factor, if: :two_factor_enabled?, only: [:create]
   before_action :set_instance_presenter, only: [:new]
+  before_action :set_body_classes
 
   def new
     Devise.omniauth_configs.each do |provider, config|
@@ -109,6 +110,10 @@ class Auth::SessionsController < Devise::SessionsController
     @instance_presenter = InstancePresenter.new
   end
 
+  def set_body_classes
+    @body_classes = 'lighter'
+  end
+
   def home_paths(resource)
     paths = [about_path]
     if single_user_mode? && resource.is_a?(User)