This example demonstrates two D3 sequential color scales by rendering rows of rectangles with varying values. The top row uses `d3.scaleSequential` with the `interpolateRdGy` interpolator, while the bottom row applies `interpolateReds` to a shifted domain. Each rectangle’s fill color maps a numeric value from a fixed range, with black outlines highlighting individual cells. The code uses `d3.scaleLinear` for positioning and renders the SVG output via D3 selections and the `style('fill')` property.