A dark-themed donut chart displays total sales by product category across 20 stores, with slices labeled by category name and percentage. Data from a CSV file is aggregated using `d3.rollups` and rendered with the reusable `pieChart()` function, which leverages `d3.pie` and `d3.arc` for the layout and `d3.scaleOrdinal` with `schemeTableau10` for coloring. Interactive tooltips appear on hover using `d3.select` and mouse events, while leader lines and a legend clarify slice values.