app/views/layouts/style_guide.html.erb
<!DOCTYPE html>
<html lang="<%= I18n.locale %>">
<head>
<title><%= t('.title') %></title>
<%= stylesheet_link_tag 'application', media: 'all' %>
<%= javascript_include_tag 'application' %>
<%= csrf_meta_tags %>
</head>
<body class="<%= controller_name %> <%= action_name %>">
<main>
<%= yield %>
</main>
</body>
</html>