如何使用CSS将两个箭头图像(upvote/downvote)叠加在一起？

<div class="upvote">
  <img src="upvote-arrow.png" alt="Upvote Arrow">
</div>
<div class="downvote">
  <img src="downvote-arrow.png" alt="Downvote Arrow">
</div>

.upvote, .downvote {
  position: relative;
}

.upvote img {
  /* 调整upvote箭头的位置 */
  top: 0;
  left: 0;
}

.downvote img {
  /* 调整downvote箭头的位置 */
  top: 0;
  left: 0;
}

.upvote img, .downvote img {
  width: 20px;
  height: 20px;
  opacity: 0.8;
}