You will need to fix the css, hide should transform from 300px to 0.

@keyframes submenu-hide {
  from {
    opacity: 1;
    transform: translateX(300px);
  }

  to {
    opacity: 0;
    transform: translateX(0);
  }
}

See working example: https://codesandbox.io/p/devbox/slide-menu-transition-p4t8mm