A checkpoint visualization confirms that JavaScript is running by rendering a plain gray rectangle alongside a text message. The `index.html` file contains embedded CSS and a script that dynamically creates a styled `<div>` element, setting its dimensions, background color, and margins before appending it to the document body. The script also logs a confirmation to the console, verifying execution. This minimal example serves as a functional test, not a data-driven graphic, and does not employ any external libraries or map-related APIs.