A red rectangle with a thick black border sits centered in an SVG canvas. The example demonstrates CSS transitions triggered by hover, causing the rectangle to gradually change its fill color to green while its stroke width expands from 20px to 100px over three seconds. The code uses plain SVG elements with inline CSS style rules, applying the `transition` property to all animated attributes. No external libraries or data sources are involved; the visualization relies solely on native SVG and CSS animation capabilities within an HTML document.