<button
  data-title="Get the best offers!"
  data-help="Call 1800-00-00-123456!"
>
  Subscribe
</button>

button {
  color: #333;
  font-size: 1.3rem;
  padding: 2rem;
  background-color: #eee;
  border: 1px solid #ddd;
  position: relative;
  transition: all ease 200ms;
}

@media (pointer: fine) {
  button:hover {
    color: #fff;
    border-color: #000;
    background-color: #333;
  }
  button:hover:after {
    top: 90%;
  	background: #aaa;
    border-radius: 0.25rem;
    content: attr(data-title);
    position: absolute;
    font-size: 0.7rem;
    padding: 0.5rem 0.8rem;
    width: max(100%, 200px);
    max-width: max-content;
  }
}

@media (pointer: coarse) {
  button:after {
    content: attr(data-title);
    display: block;
    font-size: 0.75rem;
  }
  button:hover {
    color: #ddd;
    border-color: #aaa;
    background-color: #999;
  }
}

@media (pointer: none) {
  button:before, button:after {
    display: block;
    font-size: 0.75rem;
  }
  button:after {
    content: attr(data-title);
  }
  button:before {
    content: attr(data-help);
  }
}