popover-menu.css

  .nav-mobile-toggler {
    anchor-name: --nav-toggler;
  }
  .nav-mobile {
    position-anchor: --nav-toggler;
    position-area: block-end span-inline-start;
    margin: 0.5rem 0 0 0;

    @media (prefers-reduced-motion: no-preference) {
      opacity: 0;
      transform: translateY(-0.5rem);
      transition:
        display 0.2s allow-discrete,
        overlay 0.2s allow-discrete,
        opacity 0.2s,
        transform 0.2s ease-out;
    }
  }

  .nav-mobile:popover-open {
    opacity: 1;
    transform: translateY(0);
  }

  @media (prefers-reduced-motion: no-preference) {
    @starting-style {
      .nav-mobile:popover-open {
        opacity: 0;
        transform: translateY(-0.5rem);
      }
    }
  }