A stacked bar chart compares total sales across product sub-categories, segmented by customer segment (Consumer, Corporate, Home Office). The chart uses D3.js with the `d3.nest`, `d3.layout.stack`, and `d3.legend.color` APIs to compute the stacked layout and render an interactive legend. Data is loaded from a CSV file (`data(sorted & grouped).csv`). Hover tooltips and a semi-transparent overlay highlight individual segments.