function getCoords(elem) {
    var box = elem.getBoundingClientRect();

    var body = document.body;
    var docElem = document.documentElement;

    var scrollTop = window.pageYOffset || docElem.scrollTop || body.scrollTop;
    var scrollLeft = window.pageXOffset || docElem.scrollLeft || body.scrollLeft;

    var clientTop = docElem.clientTop || body.clientTop || 0;
    var clientLeft = docElem.clientLeft || body.clientLeft || 0;

    var top  = box.top +  scrollTop - clientTop;
    var left = box.left + scrollLeft - clientLeft;

    return { top: Math.round(top), left: Math.round(left) };
}

function getElementUnderClientXY(elem, clientX, clientY) {
  var display = elem.style.display || '';
  elem.style.display = 'none';

  var target = document.elementFromPoint(clientX, clientY);

  elem.style.display = display;

  return target;
}