This example demonstrates how basic SVG shapes—circles and rectangles—can be styled and grouped using both inline attributes and CSS. It shows three sets of shapes: the first uses default black fill, the second uses explicit inline fill colors, and the third applies a `fill` attribute to a `<g>` group to style all contained shapes. The code also defines a `.highlighted` CSS class, though it is not applied to any visible element. The SVG is rendered directly in the HTML document with a fixed 960×500 viewport, using standard SVG elements and a linked external stylesheet.