This line chart shows the performance of the VPG reinforcement learning algorithm in the Walker environment over time, plotting average episode return against the number of interactions. The visualization is rendered as an SVG using D3.js v5, with the `scaleLinear`, `axisLeft`, and `axisBottom` functions for the axes, and the `line` function with `curveBasis` to create the smoothed data path. Data is loaded from a remote CSV via `d3.csv` and styled with custom CSS for labels and title.