Smooth Scroll with Offset

gistfile1

$('.scrollto').click(function() {
    if (location.pathname.replace(/^\//,'') == this.pathname.replace(/^\//,'') 
                || location.hostname == this.hostname) {
        var hashStr = this.hash.slice(1);
        var target = $(this.hash);
        target = target.length ? target : $('[name=' + hashStr +']');

        if (target.length) {
            $('html,body').animate({ scrollTop: target.offset().top - 20}, 500);
            window.location.hash = hashStr;
            return false;
        }
    }
});