This example shows a simple bar chart of letter frequencies, with clickable bars that highlight the selected letter while dimming others. The chart is built with D3 v7 inside a React component, using `scaleBand` and `scaleLinear` for positioning, `axisBottom` and `axisLeft` for axes, and SVG `rect` elements for bars. Data comes from a local CSV file loaded via `d3.csv`. A `ResizeObserver` in `useDimensions` tracks the container size, and transitions animate bar color and opacity on selection.