src/cssjanus.js
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;
	}
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;
	}
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 ; }
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
Invert the horizontal value of a background position property .