function getContentOffset(element) {
    var styles = element.ownerDocument.defaultView.getComputedStyle(element, '');
    return {
      left: element.clientLeft + parseFloat(styles.paddingLeft),
      top: element.clientTop + parseFloat(styles.paddingTop)
    };
  }
Get distance between an element's bounding-box and its content (`<iframe>` element and its document).
@param {Element} element - Target element.
@returns {{left: number, top: number}} An object has `left` and `top`.