Last week I started a series on SVG and walked through the different ways you can include SVG inside an HTML page. Because I needed to show you something that would display on your screen, the examples included a green rectangle.
One of the limitations of developing websites is that everything is fundamentally a rectangular box. We fight against it. We create non-rectangular images, we round corners, we have a variety of creative techniques to display less box-like shapes, but still behind the scenes each of these things sits in a rectangular box and other elements react to that box seen or unseen.