This line chart visualizes the relationship between engine size and average vehicle price using a sampled car dataset. The chart aggregates raw CSV data with `d3.rollup` to compute mean prices per engine size, then renders a monotone-smoothed path with `d3.line` and SVG circles for each data point. Axes use `d3.axisBottom` and `d3.axisLeft`, with price formatting as currency. Interactive hover tooltips display exact values via mouse events, all styled with a dark theme.