<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8" />
<meta http-equiv="X-UA-Compatible" content="IE=edge" />
<meta name="viewport" content="width=device-width, initial-scale=1.0" />
<title>Document</title>
</head>
<body>
<style>
.a1 {
width: 200px;
height: 200px;
background-color: chartreuse;
}
.a2 {
width: 300px;
height: 300px;
background-color: rgb(92, 95, 241);
}
</style>
<button id="btn1">修改div的class从a1改成a2</button>
<button id="btn2">修改div的class从a2改成a1</button>
<p></p>
<div id="box" class="a1"></div>
</body>
<script type="text/javascript">
var box = document.getElementById("box");
var btn1 = document.getElementById("btn1");
btn1.onclick = function () {
box.className = "a2";
};
btn2.onclick = function () {
box.className = "a1";
};
</script>
</html>
