boxes.html

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Document</title>
    <link rel="stylesheet" href="boxstyle.css">
</head>
<body>
    <div class="container">
        <div class="red in">
            <div class="blue in">
                <div class="green in">
                    <div class="yellow in">
                        <div class="green out">
                            <div class="blue out">
                                <div class="red out">
                                    <div class="white"></div>
                                </div>
                            </div>
                        </div>
                    </div>
                </div>
            </div>
        </div>
    </div>
</body>
</html>