redstoner.com/app/views/comments/_new.html.erb

<% if current_user %>
  <h3>New comment</h3>
  <%= simple_form_for [@post, @comment] do |f| %>
    <%= f.input :content, :label => false, :as => "text", :placeholder => "Comment", input_html: {class: "comment"} %>
    <%= f.submit class: "btn blue" %>
  <% end %>
<% end %>