scroll-top.txt

 .scroll{
            position : fixed;
            right : 10px;
            bottom : 10px;
            background : #fff;
            border-radius: 50%;
            padding : 10px 14px;
            color : #444;
            display : none;
            box-shadow: 0px 0px 5px 1px #ddd;
        }

	<span class="scroll">
        <i class="fas fa-arrow-up"></i>
    </span>

$(document).on('scroll',function(){
        if (document.body.scrollTop > 100 || document.documentElement.scrollTop > 100) {
            $('.scroll').css({'display':'block'})
            // mybutton.style.display = "block";
        } else {
            $('.scroll').css({'display':'none'})
            // mybutton.style.display = "none";
        }
    })

    $('.scroll').on('click',function(){
        var scrl = document.documentElement.scrollTop;

        var inter = setInterval(() => {
            document.documentElement.scrollTop -= scrl/100
            if(document.documentElement.scrollTop <= 0){
                clearInterval(inter);
            }

        }, 1);

    })