Treeview transition effect

[jeyjack]

I am using THIS SCRIPT from W3schools  but I was wondering, is there a way to add a transition effect so that when clicking on items, they are not expanded/contracted too fast but with a slide effect?

This is the actual CSS of the Treeview menù:

ul, #myUL {
  list-style-type: none;
}

#myUL {
  margin: 0;
  padding: 0;
}

.caret {
  cursor: pointer;
  -webkit-user-select: none; /* Safari 3.1+ */
  -moz-user-select: none; /* Firefox 2+ */
  -ms-user-select: none; /* IE 10+ */
  user-select: none;
}

.caret::before {
  content: "\25B6";
  color: black;
  display: inline-block;
  margin-right: 6px;
}

.caret-down::before {
  -ms-transform: rotate(90deg); /* IE 9 */
  -webkit-transform: rotate(90deg); /* Safari */'
  transform: rotate(90deg);
}
.nested {
  display: none;
}

.active {
  display: block;
}