A pseudo XY-heatmap presents a grid of gray rectangles on an SVG canvas. The visualization demonstrates a simple interactive state change where each block transitions to a red fill when the cursor hovers over it, using a CSS `:hover` pseudo-class and a `transition` property for the color change. The rect elements are manually coded with explicit `x` and `y` coordinates, creating a sparse matrix layout. The interaction is immediate rather than data-driven, as hovering changes the fill color with a fast 0.15-second transition, while the default state is a steady gray.