When using two different bodyElements, the zeroElement is reused between them causing position to be completely off

This may be related to #279.

See example: https://stackblitz.com/edit/web-platform-xvi6jy?file=script.js To reproduce, click on the left red box, then click on the right red box. Note that the positions are correct. Now clicking on the left red box again will cause the popup to be placed incorrectly.

The zeroElement in the container is being reused for calculations on the html body element in bounds.js