:nth-last-of-type(<an-plus-b> | even | odd) {
  /* ... */
}

<div>
  <span>This is a span.</span>
  <span>This is another span.</span>
  <em>This is emphasized.</em>
  <span>Wow, this span gets limed!!!</span>
  <del>This is struck through.</del>
  <span>Here is one last span.</span>
</div>

span:nth-last-of-type(2) {
  background-color: lime;
}