This example shows a hierarchical circle packing layout for a small dataset with two leaf nodes, "a" and "b", rendered as nested circles. The visualization colors leaf circles using a categorical color scale and provides customizable legends for both color and size. The code uses the D3 `hierarchy` and `pack` layout functions to compute circle positions, while custom legend components (colorLegend and sizeLegend) display the ordinal color mapping and a square-root size scale. The rendering is an SVG generated by D3 v5.