This is a React and D3.js bar chart that visualizes letter frequency data from a CSV file (seven letters with associated counts). The chart displays teal bars, and clicking a bar highlights it by changing its color and opacity while dimming others. Built with React 19 and D3 v7, the code uses D3 scales (`scaleBand`, `scaleLinear`), axes (`axisBottom`, `axisLeft`), and selections with the `.join()` pattern to render the interactive SVG. State management tracks the selected letter, triggering re-renders upon user interaction.