Cách tạo nút Back top

1. Html
<a id="back-to-top" href="#" class="btn btn-top btn-lg back-to-top" role="button" title="Lên đầu trang" data-toggle="tooltip" data-placement="left">
<span class="fa fa-chevron-up"></span>
</a>

2. Css

<style>
.back-to-top {
    cursor: pointer;
    position: fixed;
    bottom: 20px;
    right: 20px;
    display:none;
    z-index : 10000;
}
.btn-top{
color: #fff;
background-color: #12121373;
}
.btn-top:focus{
color: #fff;
}
.btn-top:hover{
color: #f8b81d;
}
</style>

3. Javascript

<script>
$(document).ready(function(){
     $(window).scroll(function () {
            if ($(this).scrollTop() > 50) {
                $('#back-to-top').fadeIn();
            } else {
                $('#back-to-top').fadeOut();
            }
        });
        // scroll body to 0px on click
        $('#back-to-top').click(function () {
            $('#back-to-top').tooltip('hide');
            $('body,html').animate({
                scrollTop: 0
            }, 800);
            return false;
        });
        
        $('#back-to-top').tooltip('show');

});
</script>