Rails 3: “field-with-errors” wrapper changes the page appearance. How to avoid this?

You should override ActionView::Base.field_error_proc. It’s currently defined as this within ActionView::Base:

 @@field_error_proc = Proc.new{ |html_tag, instance| 
   "<div class=\"field_with_errors\">#{html_tag}</div>".html_safe
 }

You can override it by putting this in your application’s class inside config/application.rb:

config.action_view.field_error_proc = Proc.new { |html_tag, instance| 
  html_tag
}

Restart rails server for this change to take effect.