height-animation.css

.element {
  max-height: 5000px; /* super high just to have something */
  opacity: 1;
  transition: max-height 1s ease-in-out, opacity 0.5s ease-in-out;
}

.element.hidden {
  visibility: hidden;
  max-height: 0px;
  opacity: 0;
  transition: max-height 0.5s cubic-bezier(0, 1, 0, 1), opacity 0.5s ease-in-out;
}