固定头部

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <style>
        .pg-header{
            height: 48px;
            background-color: greenyellow;
            color: #dddddd;
            position: fixed;
            top:0;
            right: 0;
            left: 0;
        }
        .pg-body{
            background-color: #dddddd;
            height: 5000px;
            margin-top: 50px;
        }
    </style>
</head>
<body>
    <div class="pg-header">头部</div>
    <div class="pg-body">内容</div>
</body>
</html>

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