<head>
<meta charset="UTF-8">
<title>垂直居中示例</title>
<style>.hello {height: 200px;display: flex;justify-content: center;align-items: center;background-color: red;font-size: 48px;color: #333;}
</style>
</head>
<body>
<div class="hello">hello</div>
</body>
