A dark-themed scatterplot visualizes the classic Iris dataset, plotting petal width against petal length. Each of the 150 points is colored by species—setosa in blue, versicolor in green, and virginica in red—with white strokes for contrast. Hovering over a point enlarges its stroke and displays a temporary tooltip with its coordinates. The visualization is built with D3 v4, using `d3.scaleLinear` for the x- and y-axes, `d3.axisBottom` and `d3.axisLeft` for tick marks, and SVG circles with mouse event handlers. The code also attempts to calculate a linear regression line, though the final path is not rendered correctly.