entrydns/app/views/public/pages/contact/_form.html.erb

<%= simple_form_for(@contact_form, 
    url: { action: 'contact' },
    html: { method: :post, class: 'form-horizontal' }
  ) do |f| %>
  
  <%= error_messages_for(@contact_form) %>

  <div style="display:none;">
    <%= f.text_field :nickname %>
  </div>

  <div class="inputs">
    <%= f.input :name, label: 'Your name' %>
    <%= f.input :email, label: 'Your email' %>
    <%= f.input :file, as: :file, hint: 'can be attached optionally' %>
    <%= f.input :message, as: :text, input_html: { rows: 10 } %>
  </div>

  <div class="form-actions">
    <%= f.submit 'Send', :class => 'btn btn-primary' %>
  </div>

<% end %>