app/views/devise/sessions/new.html.erb
<%= form_for(resource, :as => resource_name, :url => session_path(resource_name), :html =>{:class => "form-signin", :style => "margin-top:50px;"}) do |f| %>
<h2 class="form-signin-heading">Quango Assurance</h2>
<%= f.email_field :email, :autofocus => true, :class => "input-block-level", :placeholder => "Email Address" %>
<%= f.password_field :password, :class => "input-block-level", :placeholder => "Password" %>
<% if devise_mapping.rememberable? -%>
<label class="checkbox">
<%= f.check_box :remember_me %> Remember Me
</label>
<% end -%>
<div><%= f.submit "Sign in", :class => "btn btn-primary" %></div>
<% end %>
<div class="span4 offset4">
<%= render "devise/shared/links" %>
</div>