Making a Bar Chart
A bar chart displays population estimates for thirteen countries and two placeholder entries, with bars sized by population and colored on a red gradient. Hovering over a bar updates an HTML overlay with the country name and value. A green circle toggles an animation that transitions all bar widths between zero and their original lengths using a custom `transitionWidth` function. The visualization uses D3 v5 APIs including `scaleLinear`, `scaleBand`, `axisLeft`, `axisBottom`, and `.transition()`, with SVG rendering and data loaded from a local CSV file.