app/views/authentication/new.html.erb
<div class="well well-lg col-md-offset-4 col-md-4">
<% if alert %>
<div class="alert alert-danger">
<%= alert %>
</div>
<% end %>
<h1>Sign In</h1>
<br>
<%= form_tag signin_path do |f| %>
<% if @sign_in_error %>
<p class="text-danger">
<%= @sign_in_error %>
</p>
<% end %>
<div class="field form-group">
<div class="control-label">
<%= label_tag :email %>
</div>
<div>
<%= email_field_tag :email, '', :class => 'form-control' %>
</div>
</div>
<div class="field form-group">
<div class="control-label">
<%= label_tag :password %>
</div>
<div>
<%= password_field_tag :password, '', :class => 'form-control' %>
</div>
</div>
<div>
<%= submit_tag "Sign in", :class => "btn btn-primary" %>
</div>
<% end %>
</div>