This visualization presents a layered line chart comparing gas consumption amounts and fuel efficiency (mpg) over time. The data is loaded from a GitHub-hosted CSV file using `d3.csv`. The chart uses two overlaid line marks with independent y-axes, created via the Vega-Lite API’s `vl.layer` and `resolve` functions. Both layers encode date on the x-axis and tooltips on the data fields. The visualization is rendered with Vega-Lite, using a custom config for axis styling and colors.