Ruby on rails - bootstrap material design - Add checkboxes to simple form

I installed the Bootstrap Material Design in my Ruby on Rails application and every animation is functioning properly, but i can´t see the checkboxes. My code for the checkboxes is:

<div class='form-group'>
  <div class='control-label col-sm-2'>
  </div>
  <div class='col-sm-8'>
    <%= f.input :active, :as => :boolean, :label => false, :inline_label => true %>
  </div>
</div>

Can anyone Help me please?

Thank you all!