BUTTON 21

/* HTML */
<a href="#"><button class="button-21">Hover over me ☝️</button></a>

/* CSS */
.button-21 {
  font-size: 1em;
  font-family: monospace;
  background-color: pink;
  border: 2px solid #000;
  padding: 0.5em 0.5em;
  transition: background-color 2s ease-out;
}

.button-21:hover {
  background-color: yellow;
}