abstract：<!DOCTYPE html><html> <head> <meta charset="UTF-8"> <title></title> <script type="text/javascript" src="../jquery-3.3.1.js">
<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title></title>
<script type="text/javascript" src="../jquery-3.3.1.js">
</script>
<style type="text/css">
.a1{
width: 100px;
height: 100px;
background: pink;
}
.a2{
width: 200px;
height: 200px;
background: red;
}
</style>
</head>
<body>
<script type="text/javascript">
$(document).ready(function () {
$('.box').click(function () {
$('div').addClass('a2');
})
$('.box1').click(function () {
$('div').removeClass('a2');
})
})
</script>
<div class="a1">
</div>
<button class="box">改变颜色</button>
<button class="box1">清空</button>
</body>
</html>