span {
  position: relative;
  color: blue;
  cursor: pointer;
}
span:hover:before {
    opacity: 1;
}

span:before {
  content: attr(aria-label);
  opacity: 0;
  position: absolute;
  top: 30px;
  right: -90px;
  font-size: 14px;
  width: 100px;
  padding: 10px;
  color: #fff;
  background-color: #555;
  border-radius: 3px;
  pointer-events: none;
}

div {
  padding: 40px;
  font-size: 20px;
  font-family: sans-serif;
}