<html><head><link rel="stylesheet" href="https://www.w3schools.cn/cdnjs/ajax/libs/font-awesome/4.7.0/css/font-awesome.min.css"><style>.fa { font-size: 50px; cursor: pointer; user-select: none;}.fa:hover { color: darkblue;}</style></head><body><p>单击图标可在赞成和反对（喜欢/不喜欢）之间切换：</p><i onclick="myFunction(this)" class="fa fa-thumbs-up"></i><script>function myFunction(x) { x.classList.toggle("fa-thumbs-down");}</script></body></html>