app/views/devise/sessions/new.html.erb
<div class="panel-heading">
<h2 class="text-center">Log in</h2>
</div>
<div class="panel-body">
<%= form_for(resource, as: resource_name, url: session_path(resource_name)) do |f| %>
<div class="form-group">
<%= f.email_field :email, autofocus: true, class: 'form-control', placeholder: 'Email' %>
</div>
<div class="form-group">
<%= f.password_field :password, autocomplete: "off", class: 'form-control', placeholder: 'Password' %>
</div>
<% if devise_mapping.rememberable? -%>
<div class="checkbox">
<label>
<%= f.check_box :remember_me %>
<span class="ripple"></span>
<span class="check"></span>
Remember me?
</label>
</div>
<% end -%>
<div class="actions">
<%= f.submit "Log in", class: 'btn btn-success btn-block' %>
<%= link_to "Sign up", new_registration_path(resource_name), class: 'btn btn-primary btn-block' %><br />
</div>
<% end %>
<%= render "devise/shared/links" %>
</div>