_getElemY = function (elem, side) {
  var pos = 0;
  var elemHeight = elem.offsetHeight;

  while (elem) {
    pos += elem.offsetTop;
    elem = elem.offsetParent;
  }

  if (side === 'bottom') {
    pos = pos + elemHeight;
  }

  return pos;
}
Get elements Y position
@param  {Object | Number} elem - The element
@param  {String}          side - Elem side (top or bottom)
@return {Number}