code: def get_css(self):
          
          css = {}
  
          print_css = os.path.join(self.theme_dir, 'css', 'print.css')
  
          if not os.path.exists(print_css):
              # Fall back to default theme
              print_css = os.path.join(THEMES_DIR, 'default', 'css', 'print.css')
  
              if not os.path.exists(print_css):
                  raise IOError(u"Cannot find css/print.css in default theme")
  
          with codecs.open(print_css, encoding=self.encoding) as css_file:
              css['print'] = {
                  'path_url': utils.get_path_url(print_css, self.relative),
                  'contents': css_file.read(),
              }
  
          screen_css = os.path.join(self.theme_dir, 'css', 'screen.css')
  
          if (os.path.exists(screen_css)):
              with codecs.open(screen_css, encoding=self.encoding) as css_file:
                  css['screen'] = {
                      'path_url': utils.get_path_url(screen_css, self.relative),
                      'contents': css_file.read(),
                  }
          else:
              self.log(u"No screen stylesheet provided in current theme",
                        'warning')
  
          return css
docs: Fetches and returns stylesheet file path or contents, for both
              print and screen contexts, depending if we want a standalone
              presentation or not.