Find the offsetTop of any item by recursively looking at the parent element until parent offset is 0

findOffsetTop

  /* Finds the total offset of an item inside a window */
  var findOffsetTop = function(el) {
    var offset = el.offsetTop;
    if (el.parentNode.offsetTop !== 0) {
      offset += findOffsetTop(el.parentNode);
    }
    return offset;
  };