This example demonstrates a simple D3.js visualization: a single large yellow circle centered within an SVG canvas. It introduces fundamental SVG and D3 selection patterns by creating, styling, and positioning a circle element using `d3.select`, `svg.append`, and `.attr` methods. The code sets the circle’s radius to 200 pixels, fills it with yellow, and centers it horizontally and vertically based on the SVG’s width and height attributes. The visualization serves as a minimal, hands-on introduction to rendering SVG shapes with D3 v5.