<main>
  <button popovertarget="tooltipA">Show tooltipA</button>
</main>

<dialog id="tooltipA" popover>
  <button popovertarget="tooltipA">Hide tooltipA</button>
</dialog>

main [popovertarget] {
  anchor-name: --trigger;
}

[popover] {
  margin: 0;
  position-anchor: --trigger;
  top: calc(anchor(bottom) + 10px);
  justify-self: anchor-center;
}

/* This also works, but isn’t needed
unless you’re using the display property
[popover]:popover-open {
	...
}
*/