Html页面加回滚

<div class="top-box">
<img src="~/Content/img/youlink.jpg" width="" height="" class="youlink-img" /><br />
<img src="~/Content/img/top.gif" class="top-img" />
</div>

//根据浏览页面的高度，显示回滚标签
$(window).scroll(function () {
if ($(window).scrollTop() >= ($(window).height() - )) {
$('.top-box').fadeIn();
}
else {
$('.top-box').fadeOut();
}
});

//点击进行回滚
$(".top-img").on("click", function () {
//动画效果
$('html,body').animate({ scrollTop:  }, );
});