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/statuses_controller.rb

@@ -22,6 +22,8 @@ class StatusesController < ApplicationController
   def show
     respond_to do |format|
       format.html do
+        @body_classes = 'with-modals'
+
         set_ancestors
         set_descendants