This example demonstrates basic JavaScript and CSS integration within a simple HTML page. It writes a red-colored message and a user’s age directly into the document using `document.write`, then triggers an `alert` displaying the age variable. The code uses core DOM methods like `document.write` and the global `alert` function, with no external libraries. The page’s embedded script and external `age.js` file highlight foundational scripting patterns in a plain HTML structure, emphasizing how JavaScript can manipulate page content and interact with the user.