application.css

  #header h2#logo a {
    display: block;
    width: 159px;
    height: 38px;
    background-image: url('/images/logo.png');
    background-image: url('http://images.foobar.com/images/logo.png');
    background-repeat: no-repeat; }

application.sass (extraction)

=bgimg_tag(!image)
  - if RAILS_ENV == development
  :background-image url('/#{!image}')
  - else
  :background-image url('http://images.foobar.com/#{!image}')

h2#logo a
    :display block
    :width 159px
    :height 38px
    +bgimg_tag(images/logo.png)
    :background-repeat no-repeat