This example illustrates the foundational structure of an HTML page, displaying a centered "Hello HTML!" message using a CSS class. The code defines a `.message` style with a large font size and text alignment. It demonstrates basic HTML document setup, including a `<head>` with a `<title>`, embedded `<style>` rules, and a `<body>` containing the styled content. The example uses semantic HTML elements and CSS styling to achieve a simple, clear visual output without any JavaScript or external libraries.