Header Scroll Response - CSS / JS

<script type="text/javascript">
$(window).scroll(function(){

var a = 112;
var pos = $(window).scrollTop();
if(pos > a) {
    $("menu").css({
                position: 'fixed'
            });
}
else {
    $("menu").css({
                position: 'absolute',
                top:'600px'
            });
}
});
</script>