This example demonstrates fundamental SVG shapes and styling, including circles, a rectangle, and a line. It shows CSS-driven interactivity, where hovering over the rectangle triggers a green fill and expanded stroke width, with a smooth transition over three seconds. The code uses plain SVG elements within an HTML page, styled via CSS selectors like `rect:hover`, and relies on inline attributes such as `fill`, `stroke`, and `stroke-width`. No JavaScript or external libraries are involved; the rendering is purely static SVG with CSS transitions.