A categorical bar chart displays letter frequencies from a CSV file, with bars colored in teal and rounded corners. Clicking a bar toggles a highlight that dims other bars, revealing the selected category. The React app uses a `ResizeObserver` to track container dimensions and D3 v7 for scales, axes, and SVG rendering. Data loads via `d3.csv`, and bar interactions are handled through React state updates that trigger D3 data joins and transitions.