This interactive bar chart displays the frequency of letters from a CSV file, with bars that respond to clicks by highlighting the selected letter and dimming others. Built with React and D3 v7, it uses `scaleBand` and `scaleLinear` for axes, `axisBottom` and `axisLeft` for ticks, and a React `useDimensions` hook with `ResizeObserver` to adapt to container size. The `.join` operator efficiently updates SVG rects, while CSS transitions animate fill and opacity changes on hover and selection.