使用方法:
1、head引入css文件
<link rel="stylesheet" href="css/style.css">
2、body引入部分
<div class="bounce"> <span class="letter">1</span> <span class="letter">7</span> <span class="letter">s</span> <span class="letter">u</span> <span class="letter">c</span> <span class="letter">a</span> <span class="letter">i</span> </div>