1️⃣ ul li.bb.bb2{
}
2️⃣ ul li .bb .bb2{
}
观察1️⃣ 2️⃣有什么不同
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>测试类名</title>
<style type="text/css" media="screen">
.aa{
background-color: red;
}
ul li.bb{
background-color: blue;
}
ul li.bb.bb2{
background-color: pink;
}
ul li.bb2.bb3{
background-color: yellow;
}
</style>
</head>
<body>
<div>
<ul>
<li class="aa">1</li>
<li class="bb bb2 bb3">2</li>
<li>3</li>
<li>4</li>
<li>5</li>
</ul>
</div>
</body>
</html>