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

!!!
%html{ lang: I18n.locale }
  %head
    %meta{ 'content' => 'text/html; charset=UTF-8', 'http-equiv' => 'Content-Type' }/
    %meta{ charset: 'utf-8' }/
    %title= safe_join([yield(:page_title), Setting.default_settings['site_title']], ' - ')
    %meta{ content: 'width=device-width,initial-scale=1', name: 'viewport' }/
    = stylesheet_pack_tag 'common', media: 'all', crossorigin: 'anonymous'
    = stylesheet_pack_tag Setting.default_settings['theme'], media: 'all', crossorigin: 'anonymous'
    = javascript_pack_tag 'common', crossorigin: 'anonymous'
    = javascript_pack_tag 'error', crossorigin: 'anonymous'
  %body.error
    .dialog
      .dialog__illustration
        %img{ alt: Setting.default_settings['site_title'], src: '/oops.png' }/
      .dialog__message
        %h1= yield :content