A single gray circle follows the mouse cursor across an SVG canvas that fills the browser window. The demonstration shows how D3 v7 event handling can drive direct attribute updates on SVG elements. The code appends an SVG and circle using d3.select and selection.append, then listens for mousemove events on the SVG, updating the circle’s cx and cy coordinates from the event’s x and y properties. No external data source is used; the visualization relies purely on user interaction with the rendered vector graphic.