Of course I know this kind of technique :).
Although I consider this as useless, because I can’t change the color of the background or border without screwing the rest of it. What I mean is: I can’t have diagonal borders. I did know about the triangle trick, but unfortunatly that allows only one-colored boxes.
As I said, maybe SVG could be a possible solution to get full control of the shape.
I do not really care about that in the end it is a rectangular box, but I would love to create the boxdesign without being restricted to one color. I hope you get an idea of what I try to achieve.
Thank you a lot and best regards.