<details> animation support

details-animation-support.css

@media (prefers-reduced-motion: no-preference) {
  details {
    transition: 0.3s ease-in-out;

    @supports (interpolate-size: allow-keywords) {
      interpolate-size: allow-keywords;

      &::details-content {
        block-size: 0;
        opacity: 0;

        transition: 0.3s ease-in-out allow-discrete;
        overflow-y: hidden;
      }

      &[open]::details-content {
        block-size: auto;
        opacity: 1;
      }
    }
  }
}