This example renders a single circle centered within an SVG element created by D3’s selection join pattern. The program uses `d3.select` and the `join` method to manage both the SVG and circle, setting the circle’s `cx` and `cy` attributes to the container’s measured width and height. Its primary purpose is demonstrating an immutable update structure, as described in the README, where state changes follow Redux-style patterns. The visualization does not respond to mouse events; it shows a static, fixed-radius circle.