A static legend template renders five color-coded grade categories—A, B, C, D, and F—as labeled rectangles inside a bordered box. Built with d3.v4, the code appends SVG rectangles and text elements using chained `attr` calls, with fixed coordinates and fill colors (green, steelblue, dark blue, light blue, and red). The example includes two buttons that reference undefined update functions, indicating an intended but unimplemented interactivity; currently, the visualization displays only the legend without any data-driven elements.