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/* ScrollUp Button */

$(window).scroll(function(){
    if ($(this).scrollTop() > 100) {
        $('.scrollup').fadeIn();
    } else {
        $('.scrollup').fadeOut();
    }
});

$('.scrollup').click(function(){
    $('html, body').animate({ scrollTop: 0 }, 600);
    return false;
});

.scrollup {
    display: none;
    background: url("img/icons.png") no-repeat scroll -53px -187px transparent;
    position: fixed;
    bottom: 20px;
    right: 15px;
    height: 29px;
    width: 29px;
    cursor: pointer;
    z-index: 99999;
}

<span class="scrollup"></span>