Это делается примерно так на jQuery:
https://jsfiddle.net/IonDen/v8ubpuee/<div class="paravozik">
Choo-choo
</div>
.paravozik {
position: fixed;
bottom: 0; left: 0;
width: 100px;
height: 50px;
background: #000;
}
var $win = $(window),
$paravozik = $(".paravozik"),
top = 0,
height = $(document.body).innerHeight(),
vpHeight = 0,
percent = 0;
$win.on("scroll", function () {
top = $win.scrollTop();
vpHeight = $win.innerHeight();
percent = top / (height - vpHeight) * 100;
$paravozik[0].style.left = percent + "%";
});
