JSFiddle - React, Tailwind, and code Playground

HTML

<div id="scroll"></div>
<div id="bigBlock"></div>

CSS

body {
    padding:0px;
    margin:0px;
}
#scroll {
    background:green;
    height:50px;
    width:50px;
    position:fixed;
    right:0px;
}
#bigBlock {
    height:5000px;
}

JavaScript

$(document).scroll(function () {
    var $document = $(this);
    var $block = $('#scroll');
    var blockHeight = $block.height();
    var bodyHeight = $document.height();
    var viewportHeight = $(window).height();
    var scrollPosition = $document.scrollTop();
    var blockPosition = (scrollPosition / (bodyHeight - viewportHeight) * (viewportHeight-blockHeight));
    $block.css('top', Math.round(blockPosition) + 'px');
});