box_model_sizing.html

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>box model and box-sizing</title>
    <style>
        * {
            margin: 0;
        }

        body {
            --color: #333333;
            --border-color: rgb(151, 201, 244);
            --background-color: rgb(122, 183, 237);
            font-family: Arial, Helvetica, sans-serif;
            font-weight: 500;
            margin: 0.3rem;
        }

        .container {
            box-sizing: content-box;
            background-color: var(--background-color);
            margin: 10px;
            padding: 4px;
            width: 300px;
            height: 30vh;
            border: 2px solid var(--border-color);
        }
    </style>
</head>
<body>
    <div class="container"></div>
</body>
</html>