This interactive bar chart visualizes letter-frequency data loaded from a CSV file, highlighting selected bars through color and opacity changes. Built with React 19 and D3 v7, it uses `scaleBand` and `scaleLinear` for axes, `ResizeObserver` for responsive sizing, and D3 selections with `join` for rendering. Clicking a bar toggles its selection state, dimming non-selected bars to emphasize the chosen category.