Artем,
<!DOCTYPE html>
<html>
<head>
<style>
.scroller
{ position:fixed;
top:10px;
left:0px;
width:50px;
height:50px;
background-color:red
}
</style>
<script src="https://ajax.googleapis.com/ajax/libs/jquery/1.12.0/jquery.min.js"></script>
<script type="text/javascript">
$(function () {
var element = $('#back-top');
$(window).scroll(function () {
element.css('left', $(this).scrollTop() * window.innerWidth / $("#container").height() + "px");
});
});
</script></head>
<body>
<div id="container" style="position:absolute;width:100%;height:1500px"></div>
<div id="back-top" class="scroller"></div>
</body>
</html>