This example displays a treemap visualization of hierarchical data using D3 v5’s `d3.hierarchy` and `d3.treemap` layouts. The SVG renders nested rectangles sized proportionally to node values, with labels for named leaves and empty labels for internal branches. The code manually constructs the dataset in `index.js`, sums values via `root.sum`, and applies layout properties like `paddingOuter`. Rectangles and text are appended into grouped `<g>` elements, with styling from `styles.css` using royal blue fills and white strokes.