This example visually demonstrates how CSS classes and inline presentation attributes combine to style SVG shapes such as circles, rectangles, lines, and paths. The markup uses plain SVG elements within a single `svg` container, with styling applied through both inline attributes like `fill` and `stroke-width` and a CSS class (`.lines`) that sets stroke properties. The code relies on native SVG APIs and CSS, with a minimal JavaScript file that writes "Hello world" into the page. The rendering approach is direct SVG, showing how grouped elements (`<g>`) can inherit and override visual properties.