Answers for "transition display block and none"

css display none transition

div {
  border: 1px solid #eee;
}
div > ul {
  visibility: hidden;
  opacity: 0;
  transition: visibility 0s, opacity 0.5s linear;
}
div:hover > ul {
  visibility: visible;
  opacity: 1;
}

css display none transition

div > img {
	visibility: hidden;
    opacity: 0;
    height: 0;
    width: 0;
}

div:hover > img {
	visibility: visible;
    opacity: 1;
    height: auto;
    width: 4rem;
    transition: all 0.5s, opacity 2s;
}