you tagged this as 'jQuery' so i assume you would accept a jQuery solution: it is much simpler and shorter.
you didnt provide your html markup so i dont know whats going on in your page, but you could do something like that:
$("#button").click(function() {
$('body').animate({
scrollTop: $("#div7").offset().top +100
}, 1000);
});
here is an example for you: Fiddle