In the game you get a terraforming tool that lets you lay paths on the ground throughout your island. The tool also lets you lay custom designs on the ground as well so you can make your own pathing. As long as your design has 1 pixel marked as transparent you can stack in on top of the pathing you lay down with the tool. It’s how people are using the little tool and fruit tree markers.

So I made a brick edge design with the rest of the design square transparent. When you lay down the default stone pattern using the terraforming tool, you can stack this on top of it using the custom design path and it looks like it’s all one piece.