A single red rectangle with a black border animates smoothly when hovered, transitioning its fill color to green and expanding its stroke width over three seconds. This simple example demonstrates SVG animation achieved through CSS transitions, applied directly to the `rect` element using the `transition: all 3000ms` property. The page is a bare HTML document with embedded CSS and JavaScript, showcasing how CSS can drive SVG property changes without explicit JavaScript animation logic. The HTML includes a minimal SVG canvas of 960 by 500 pixels, with the rectangle's styling and hover state defined entirely in the stylesheet.