This interactive bar chart visualizes the frequency distribution of letters A through G, using a categorical x-axis and a linear count y-axis with gridlines. Built with React and D3 v7, the visualization loads data from a CSV file and renders SVG elements using the `d3.scaleBand` and `d3.scaleLinear` scales. Users can click individual bars to highlight selections, which trigger React state updates that alter bar colors and opacities. The chart includes labeled axes, a title, and smooth CSS transitions for interactive feedback.