function isFixed(element) {
  if (element === root.document.body) {
    return false
  }
  if (getStyleComputedProperty(element, 'position') === 'fixed') {
    return true
  }
  return element.parentNode ? isFixed(element.parentNode) : element
}
Check if the given element is fixed or is inside a fixed parent
@function
@ignore
@argument {Element} element
@argument {Element} customContainer
@returns {Boolean} answer to "isFixed?"