:is(.popover) {
  --speed: 150ms;

  opacity: 0;
  transition:
    display var(--speed) allow-discrete,
    opacity var(--speed),
    overlay var(--speed) allow-discrete;

  &[open] {
    opacity: 1;
  }

  @starting-style {
    &[open] {
      opacity: 0;
    }
  }
}