app/views/devise/sessions/new.html.erb
<br />
<div class="container">
<div class="row justify-content-md-center">
<div class="col-12 col-md-4">
<div class="card">
<div class="card-block">
<h2 class="card-title">Log in</h2>
<%= form_for(resource, as: resource_name, url: session_path(resource_name)) do |f| %>
<div class="field form-group">
<%= f.label :email %><br />
<%= f.email_field :email, class: 'form-control', autofocus: true %>
</div>
<div class="field form-group">
<%= f.label :password %><br />
<%= f.password_field :password, class: 'form-control', autocomplete: "off" %>
</div>
<% if devise_mapping.rememberable? -%>
<div class="field">
<%= f.check_box :remember_me %>
<%= f.label :remember_me %>
</div>
<% end -%>
<div class="actions">
<%= f.submit "Log in", class: 'btn btn-primary btn-block' %>
</div>
<% end %>
<br />
<%= render "devise/shared/links" %>
<br />
<%= link_to "Sign in with Facebook", user_facebook_omniauth_authorize_path, class: "btn btn-primary btn-block" %>
</div>
</div>
</div>
</div>
</div>