JSFiddle - React, Tailwind, and code Playground

by Kocsten

HTML

<div id="back-top">
    <center>
        <a title="Вверх" id="backop" href="#top">
            <img src="http://zornet.ru/_ld/52/94331831.png" />
        </a>
        <font color="#000000" size="3"> 
        <span id="pix">0</span>%</font>
    </center>
</div>

CSS

#back-top {
    position: fixed;
    width: 50px;
    height: 100px;
    z-index: 6;
    right: 25px;
    bottom:0;
    background-color: transparent;
    display: block;
    background-position: initial initial;
    background-repeat: initial initial;
}

body {
    height:3000px
}

JavaScript

$(window).scroll(function () {
    var s = $(window).scrollTop();
    var f = $(document).height() - $(window).height();
    var d = s / f * 100;
    var p = Math.round(d);
    $("#pix").text(p);
});