code: function calculateNewBackgroundPosition( match, pre, value ) {
  		var idx, len;
  		if ( value.slice( -1 ) === '%' ) {
  			idx = value.indexOf( '.' );
  			if ( idx !== -1 ) {
  				// Two off, one for the "%" at the end, one for the dot itself
  				len = value.length - idx - 2;
  				value = 100 - parseFloat( value );
  				value = value.toFixed( len ) + '%';
  			} else {
  				value = 100 - parseFloat( value ) + '%';
  			}
  		}
  		return pre + value;
  	}
docs: Invert the horizontal value of a background position property.
  
  @private
  @param {string} match Matched property
  @param {string} pre Text before value
  @param {string} value Horizontal value
  @return {string} Inverted property