unit-less, interpreted as pixels\n   * - `%` or `%r`, percentage relative to the length of the reference element\n   * - `%p`, percentage relative to the length of the popper element\n   * - `vw`, CSS viewport width unit\n   * - `vh`, CSS viewport height unit\n   *\n   * For length is intended the main axis relative to the placement of the popper.<br />\n   * This means that if the placement is `top` or `bottom`, the length will be the\n   * `width`. In case of `left` or `right`, it will be the `height`.\n...