Well...that's one of the downsides of a CSS-only tooltip library. Hint.css (or any CSS library) creates tooltips with :before & :after pseudo elements, "inside" the target element. So if any parent above it has overflow hidden, tooltips can get clipped off. Only solution here is to position (top-left, top-right....etc etc) the tooltip in a way where it can't get clipped, if at all there is such a position for your case.
Another thing you could do, make your tooltip smaller with the size modifiers (hint--small etc). In your specific case, I would suggest make it hint--medium and position it with hint--bottom-right, like so: