CSS Box Model

The CSS box model describes how elements are structured in terms of content, padding, border, and margin. 

<!DOCTYPE html>
<html>
<head>
    <style>
        .box {
            width: 200px;
            padding: 10px;
            border: 5px solid black;
            margin: 20px;
        }
    </style>
</head>
<body>
    <div class="box">This is a box!</div>
</body>
</html>