modal.html.erb

 <!--Modal box-->
  <div class="modal fade" id="login" role="dialog">
    <div class="modal-dialog modal-sm">

      <!-- Modal content no 1-->
      <div class="modal-content">
        <div class="modal-header">
          <button type="button" class="close" data-dismiss="modal">&times;</button>
          <h4 class="modal-title text-center form-title">Login</h4>
        </div>
        <div class="modal-body padtrbl">

          <div class="login-box-body">
            <p class="login-box-msg">Sign in to start your session</p>
            <div class="form-group">
              <%= form_for resource, as: resource_name, url: session_path(resource_name) do |f| %>
               <div class="form-group has-feedback">
                  <!----- username -------------->
                  <%= f.email_field :email, placeholder: 'E-mail', id:'loginid', class:'form-control', autofocus: true %>
                  <span style="display:none;font-weight:bold; position:absolute;color: red;position: absolute;padding:4px;font-size: 11px;background-color:rgba(128, 128, 128, 0.26);z-index: 17;  right: 27px; top: 5px;"
                    id="span_loginid"></span>
                  <!---Alredy exists  ! -->
                  <span class="glyphicon glyphicon-user form-control-feedback"></span>
                </div>
                <div class="form-group has-feedback">
                  <!----- password -------------->
                  <input class="form-control" placeholder="Password" id="loginpsw" type="password" autocomplete="off" />
                  <span style="display:none;font-weight:bold; position:absolute;color: grey;position: absolute;padding:4px;font-size: 11px;background-color:rgba(128, 128, 128, 0.26);z-index: 17;  right: 27px; top: 5px;"
                    id="span_loginpsw"></span>
                  <!---Alredy exists  ! -->
                  <span class="glyphicon glyphicon-lock form-control-feedback"></span>
                </div>
                <div class="row">
                  <div class="col-xs-12">
                    <div class="checkbox icheck">
                      <label>
                          <% if devise_mapping.rememberable? -%>
                            <%= f.check_box :remember_me, id:"loginrem" %>
                           <%= f.label :remember_me, 'Lembre-me' %>
                          <% end -%>
                      </label>
                    </div>
                  </div>
                  <div class="col-xs-12">
                    <%= f.submit "Login",  class: 'btn btn-green btn-block btn-flat' %>
                  </div>
                </div>
              <% end %>
            </div> 
              <%= render "devise/shared/links" %>
          </div>
        </div>
      </div>

    </div>
  </div>
  <!--/ Modal box-->