How to decorate walls and floors

[76561199797156241]

I was joining random people's supermarket when I came across a person's supermarket who had walls and floors painted pink and it had designs.
Can someone tell me how to do so? I cannot find anything useful in the build menu.

Thanks in advance.

[[U1] Lauriel]

You need to own the DLC, if you already do, you just need use the green tablet in the "cool room"