Three SVG circles and one rectangle demonstrate basic shape primitives on a fixed 1000px canvas. The circles use default black fill, an explicit red fill, and a green fill with varying radii, while the rectangle combines gray fill, a blue stroke, and a 10px stroke-width. Rendered directly via the `<svg>` element, the example uses no external libraries, relying instead on the browser’s native scalable vector graphics support. The code illustrates how shape attributes like `cx`, `cy`, `r`, `x`, `y`, `width`, `height`, and `stroke` control geometry and styling.