code: function showBackdrop(scope, element, options) {
  
        if (options.disableParentScroll) {
          // !! DO this before creating the backdrop; since disableScrollAround()
          //    configures the scroll offset; which is used by mdBackDrop postLink()
          options.restoreScroll = $mdUtil.disableScrollAround(element, options.parent);
        }
  
        if (options.hasBackdrop) {
          options.backdrop = $mdUtil.createBackdrop(scope, "md-dialog-backdrop md-opaque");
          $animate.enter(options.backdrop, options.parent);
        }
  
        /**
         * Hide modal backdrop element...
         */
        options.hideBackdrop = function hideBackdrop($destroy) {
          if (options.backdrop) {
            if ($destroy) options.backdrop.remove();
            else              $animate.leave(options.backdrop);
          }
  
  
          if (options.disableParentScroll) {
            options.restoreScroll && options.restoreScroll();
            delete options.restoreScroll;
          }
  
          options.hideBackdrop = null;
        };
      }
docs: Show modal backdrop element...