This bar chart displays the frequency distribution of letters from a small CSV dataset. Built with React and D3 v7, it uses `scaleBand` and `scaleLinear` to position bars along categorical and numeric axes, with `axisBottom` and `axisLeft` rendering ticks and gridlines. Clicking a bar toggles its selection, changing its fill color and dimming others via a `ResizeObserver`. The chart re-renders responsively through React state management and D3’s data join pattern.