How to make div follow scrolling smoothly with jQuery?

Question

In my container there are sections/boxes, but the last one of these boxes should follow scrolling when none of the other boxes are visible.

So, when user sc

Answer 1

That code doesn't work very well i fixed it a little bit

var el = $('.caja-pago');
var elpos_original = el.offset().top;

 $(window).scroll(function(){
     var elpos = el.offset().top;
     var windowpos = $(window).scrollTop();
     var finaldestination = windowpos;
     if(windowpos