:active

<p>This paragraph contains a link:
  <a href="#">This link will turn red while you click on it.</a>
  The paragraph will get a gray background while you click on it or the link.
</p>

a:link { color: blue; }          /* Unvisited links */
a:visited { color: purple; }     /* Visited links */
a:hover { background: yellow; }  /* Hovered links */
a:active { color: red; }         /* Active links */

p:active { background: #eee; }   /* Active paragraphs */

<form>
  <label for="my-button">My button: </label>
  <button id="my-button" type="button">Try Clicking Me or My Label!</button>
</form>

form :active {
  color: red;
}

form button {
  background: white;
}