mastodon/app/views/layouts/application.html.haml

!!! 5
%html
  %head
    %meta{:content => "text/html; charset=UTF-8", "http-equiv" => "Content-Type"}/
    %title
      = "#{yield(:page_title)} - " if content_for?(:page_title)
      Mastodon
    = stylesheet_link_tag    'application', media: 'all'
    = javascript_include_tag 'application'
    = csrf_meta_tags
    = yield :header_tags
  %body{ class: @body_classes }
    = content_for?(:content) ? yield(:content) : yield