It looks like the “overflow” including overflow-x and overflow-y have been removed from AMP and thus does not work anymore. I’m currently looking for work-around.
Bumping this thread because I think it’s important. If I am not wrong (could be, nobody’s perfect), the overflow CSS property is not working with the actual Publii’s AMP template. As far as I know, the overflow is used for the HTML tables and it’s getting truncated on small screens (smartphones) thus hiding important data from the users. I looked for an alternative to fix the issue but my attempts weren’t successful because of AMP’s limitations.