A single red rectangle with a thick black stroke animates smoothly when hovered. The example uses CSS transitions on the `rect` element, defining a 1000ms transition for all properties. On hover, the fill changes to lightblue and the stroke width increases from 20px to 50px. This demonstrates how SVG elements can leverage standard CSS for declarative animation, with the rectangle placed at (250, 100) within a 960 by 500 viewport.