<html>
<head>
    <style>
        body {
            margin: 0;
        }

        html:before {
            content: '';
            background: blue;
            margin: 10px;
            width: 200px;
            height: 200px;
            position: fixed;
            z-index: -1;
        }
        
        html {
            background-image: linear-gradient(white, white);
            background-attachment: fixed;
            background-position: 50% 50%;
            background-size: 400px 400px;
            background-color: red;
        }
    </style>
</head>
<body>
</body>
</html>