Ngôn ngữ Html

1. Tạo mã HTML
<a href="#" class="cd-top">Back To Top</a>

2. Tạo Css
 
/* back to top */
a.cd-top {
display: inline-block;
height: 40px;
width: 40px;
position: fixed;
bottom: 10px;
right: 10px;
box-shadow: 0 0 10px rgba(0, 0, 0, 0.05);
/* image replacement properties */
overflow: hidden;
text-indent: 100%;
white-space: nowrap;
background: #3097D1 url("https://thinhweb.com/wp-content/themes/thinhweb/images/cd-top-arrow.svg") no-repeat center 50%;
visibility: hidden;
opacity: 0;
-webkit-transition: opacity .3s 0s, visibility 0s .3s;
-moz-transition: opacity .3s 0s, visibility 0s .3s;
transition: opacity .3s 0s, visibility 0s .3s;
}
a.cd-top.cd-is-visible, a.cd-top.cd-fade-out, .no-touch a.cd-top:hover {
-webkit-transition: opacity .3s 0s, visibility 0s 0s;
-moz-transition: opacity .3s 0s, visibility 0s 0s;
transition: opacity .3s 0s, visibility 0s 0s;
}
a.cd-top, a.cd-top:visited, a.cd-top:hover {
color: #CCCCCC;
text-decoration: none;
}
a.cd-top.cd-is-visible {
/* the button becomes visible */
visibility: visible;
opacity: 1;
}
a.cd-top.cd-fade-out {
/* if the user keeps scrolling down, the button is out of focus and becomes less visible */
opacity: 1;
}

3. Tạo JavaScript

jQuery(document).ready(function($){
// browser window scroll (in pixels) after which the "back to top" link is shown
var offset = 300,
//browser window scroll (in pixels) after which the "back to top" link opacity is reduced
offset_opacity = 1200,
//duration of the top scrolling animation (in ms)
scroll_top_duration = 700,
//grab the "back to top" link
$back_to_top = $('.cd-top');

//hide or show the "back to top" link
$(window).scroll(function(){
( $(this).scrollTop() > offset ) ? $back_to_top.addClass('cd-is-visible') : $back_to_top.removeClass('cd-is-visible cd-fade-out');
if( $(this).scrollTop() > offset_opacity ) {
$back_to_top.addClass('cd-fade-out');
}
});

//smooth scroll to top
$back_to_top.on('click', function(event){
event.preventDefault();
$('body,html').animate({
scrollTop: 0 ,
}, scroll_top_duration
);
});

});