A single red circle on a black background demonstrates fundamental SVG styling and interaction. The circle is drawn with a thick white stroke and responds to hover by gradually transitioning its fill to green and expanding its stroke width over three seconds. The example uses plain SVG elements with CSS rules for the shape’s initial appearance and the `:hover` state, leveraging the `transition` property for animation. No external libraries are used; the markup and styling are entirely self-contained in the HTML file.