Build a heatmap grid where each cell's background color reflects its intensity or activity value.
Create a grid of cells, each with a numeric value. Cells with higher values should have a darker or stronger background color.
Map each value to a color intensity (e.g., using an opacity or color scale) and apply it to the cell background.
Optionally add a legend showing the value-to-color mapping.
Test that cells with different values show clearly distinguishable colors.
