代码
提交代码
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=`, initial-scale=1.0">
<title>Document</title>
<style>
.demo:only-child{
color:#fff;
background: red;
padding:10px;
}
</style>
</head>
<body>
<div class="demo">慕课网</div>
<div class="demo">慕课网</div>
</body>
</html>
运行结果