: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>

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

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

<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;
}