This stacked bar chart visualizes the percentage distribution of grades (A, B, C, D) across five school subjects, with each bar segment color-coded by grade category. The chart uses `d3.csv` to load the data, `d3.stack` to compute cumulative values, and `d3.scaleBand` with `d3.scaleLinear` to map subjects and percentages. Hovering over a segment reveals a tooltip showing the grade and its percentage. SVG rectangles are rendered using D3's `selectAll` and `join` operations, with axes and labels drawn via `d3.axisLeft` and `d3.axisBottom`.