A stacked bar chart displays the percentage distribution of letter grades (A through F) across six classes. The code uses D3 v7 with `d3.stack` and `d3.scaleOrdinal` to construct the visualization. Tooltips reveal exact percentages on mouseover via `d3.select` and HTML injection. The chart renders as SVG, sourcing data from a local CSV file, with custom margins and axes created through `d3.axisBottom` and `d3.axisLeft`.