code: def _chosen_css(self):
          
          css = render_to_string(self.css_template, {})
          for sprite in self.chosen_sprites:  # rewrite path to sprites in the css
              css = css.replace(sprite, settings.STATIC_URL + "img/" + sprite)
          return css
docs: Read the minified CSS file including STATIC_URL in the references
          to the sprite images.