This example visualizes BMW car sales by year using an area chart with a blue filled region, a yellow line, and orange circular points. The chart aggregates annual sales data from a CSV file via `d3.csv`, then rolls up values with `d3.rollup`. It uses `d3.area` with `curveMonotoneX` to generate the filled shape and `d3.line` for the stroke. SVG rendering includes grid lines, axes, and a hover tooltip that updates through mouse events. The animation capability stems from D3 transitions applied to the tooltip’s opacity.