A minimal Observable notebook demonstrates hot reloading by displaying a large, centered “Hello World!” message. The example uses vanilla JavaScript to set the container’s inner HTML with an inline style for a font size of 217 pixels. It highlights a simple interaction where alt-dragging the number changes the font size, though the code shows only the static render. The visualization relies on the Observable runtime’s `main` function and standard DOM manipulation, with no external charting libraries or data sources.