如何摆脱重叠svg形状的发际线

I am using d3 and SVG to draw a rectangle. I then draw a different rectangle that is smaller and a different color inside the first rectangle. When I change the smaller rectangle to the same color as the bigger one you can see a white outline of where the smaller rectangle was. What is the bet way to fix this so that the smaller one just blends into the bigger one?I am using d3 and SVG to draw a rectangle. I th