lib/generators/layout/install/templates/simple-application.html.erb

<!DOCTYPE html>
<html>
  <head>
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title><%%= content_for?(:title) ? yield(:title) : "<%= app_name.underscore.titleize %>" %></title>
    <meta name="description" content="<%%= content_for?(:description) ? yield(:description) : "<%= app_name.underscore.titleize %>" %>">
    <%%= stylesheet_link_tag 'application', media: 'all', 'data-turbolinks-track' => 'reload' %>
    <%%= javascript_include_tag 'application', 'data-turbolinks-track' => 'reload' %>
    <%%= csrf_meta_tags %>
  </head>
  <body>
    <header>
      <%%= render 'layouts/navigation' %>
    </header>
    <main role="main">
      <%%= render 'layouts/messages' %>
      <%%= yield %>
    </main>
  </body>
</html>