If you mean that you want to make something with the same kind of style, only with a black rectangle instead of the green one, where you have a blending two rectangles... I don't think you can have a pure black rectangle, but you could have one that ends up grey.
Make your two overlapping rectangles, where the green one is replaced by black.
First, try simply reducing the opacity of that rectangle. If that gives you what you want, then great. (You can reduce the opacity of a selected object by clicking on the arrow to the left of the number 100 at the top of the Layer panel and dragging the slider or clicking on the nunber and typing in a different percentage value.)
You can also try changing the blending mode in addition to lowering the opacity. Some will enhance the effect, some won't be at all what you want. Experiment. The blend mode is drop down box is also at the top of the Layers panel and the default is Normal.