右下角点击页面回顶部组件

<a id="goTop" class="go-top" href="#header">
    <span class="go-top-inner"></span>
</a>

.go-top {
    background: url("../img/xxx.png") no-repeat scroll left top transparent;
    bottom: 65px;
    color: #444444;
    display: none;
    height: 50px;
    margin-left: 510px;
    position: fixed;
    right: 160px;
    text-align: center;
    width: 50px;
}
.go-top:hover {
    background-position: -50px top;
}

<!-- 页面回顶 -->
var gotop = $('#goTop');
gotop.click(function() {　　
    $("html,body").animate({ scrollTop: 0 }, 200);　　
    return false;
});
$(window).scroll(function() {
    if (gotop.offset().top > window.innerHeight) {　　
        gotop.show();
    }　　　
    else {　　
        gotop.hide();
    }　　
});