new.html.erb

<h2>Войти</h2>

<%= form_for(resource, as: resource_name, url: session_path(resource_name), :html => {:class => "form-horizontal"}) do |f| %>

  <div class="form-group">
    <div class="col-lg-8">
      <%= f.label "Почта" %>
      <%= f.email_field :email, autofocus: true, class: "form-control", placeholder: "почта" %>
    </div>
  </div>

  <div class="form-group">
    <div class="col-lg-8">
      <%= f.label "Пароль" %>
      <%= f.password_field :password, autocomplete: "off", class: "form-control", placeholder: "пароль" %>
    </div>
  </div>

  <%= f.submit "Войти", class: "btn btn-primary" %>
  
  <% if devise_mapping.rememberable? -%>
    <%= f.check_box :remember_me %>
    <%= f.label :remember_me %>
  <% end %>

<% end %>