A bar chart displays counts across seven letters (A through G), with bars colored in teal that dim to 40% opacity when a letter is deselected. Clicking a bar toggles its selection, darkening the active bar. The chart is built with React and D3 v7, using `scaleBand` and `scaleLinear` for positioning, `axisBottom` and `axisLeft` for axes with gridlines, and SVG for rendering. Data loads from a CSV file, and a `ResizeObserver` handles responsive dimensions.