Simple back to top

back-top-top.js

/* 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
		);
	});

});

index.html

<!-- HTML -->

<a href="#0" class="cd-top"><i class="fa fa-chevron-up" aria-hidden="true"></i></a>

style.css

/* CSS */
a.cd-top {
    display: block;
    height: 40px;
    width: 40px;
    position: fixed;
    bottom: 40px;
    right: 10px;
    box-shadow: 0 0 10px rgba(0, 0, 0, 0.05);
    overflow: hidden;
    white-space: nowrap;
    visibility: hidden;
    opacity: 0;
    background-color: #42AAE0;
    -webkit-transition: opacity 0.3s 0s, visibility 0s 0.3s;
    -moz-transition: opacity 0.3s 0s, visibility 0s 0.3s;
    transition: opacity 0.3s 0s, visibility 0s 0.3s;
    text-align: center;
    line-height: 38px;
    color: #fff;
    font-size: 18px;
}
a.cd-top.cd-is-visible, .cd-top.cd-fade-out, .no-touch .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.cd-is-visible {
  visibility: visible;
  opacity: 1;
}
.no-touch a.cd-top:hover {
    background-color: #42AAE0;
    opacity: 1;
}
a.cd-top:hover, a.cd-top:focus {
    color: #fff;
}