This example demonstrates how to implement zoom and pan interactions on an SVG canvas. The visualization displays a single green circle centered in the viewport, with the zoom behavior applied directly to the SVG group element. The code uses the D3 v4 zoom API via `d3.zoom().on("zoom", zoomfn)` to handle mouse and touch events, and the zoom function applies the event transform to the group. A circle is rendered at the center using `svg.append("circle")`, and the zoom handler updates the group’s `transform` attribute while also calling `svg.scale(4)`, which scales the entire group by a fixed factor. The SVG fills the browser window.