Fix container regression (#6531)

* Update public.html.haml

* Update auth.html.haml

* Update modal.html.haml

app/views/layouts/auth.html.haml

@@ -2,7 +2,7 @@
   = javascript_pack_tag 'public', integrity: true, crossorigin: 'anonymous'
 
 - content_for :content do
-  .container
+  .container-alt
     .logo-container
       %h1
         = link_to root_path do

app/views/layouts/modal.html.haml

@@ -11,7 +11,7 @@
       = link_to destroy_user_session_path, method: :delete, class: 'logout-link icon-button' do
         = fa_icon 'sign-out'
 
-  .container= yield
+  .container-alt= yield
   .modal-layout__mastodon
     %div
 

app/views/layouts/public.html.haml

@@ -2,7 +2,7 @@
   = javascript_pack_tag 'public', integrity: true, crossorigin: 'anonymous'
 
 - content_for :content do
-  .container= yield
+  .container-alt= yield
   .footer
     - if !user_signed_in? && single_user_mode?
       %span.single-user-login