code: def _css_background(self, **kwargs):
          
  
          # Get the 1x and 2x renditions
          img_1x, img_2x, _ = self._get_renditions(kwargs)
  
          tmpl = 'background-image: url("{s1x}");'
          if img_1x != img_2x:
              image_set = 'image-set(url("{s1x}") 1x, url("{s2x}") 2x)'
              tmpl += 'background-image: {ss};background-image: -webkit-{ss};'.format(
                  ss=image_set)
          return tmpl.format(s1x=img_1x, s2x=img_2x)
docs: Get the CSS specifiers for this as a hidpi-capable background image