create animation in css when you enter another element code example

Example 1: start animation with javascript

element.addEventListener("click", function(e){
  element.classList.remove("anim");
  setTimeout(() => element.classList.add("anim"), 0);
}, false);

Example 2: css tricks transition

div {
  transition: all 0.5s ease;
  background: red;
  padding: 10px;
}
div:hover {
  background: green;
  padding: 20px;
}