I marked out 4 disks and then marked 3 of them into hoops.
Cut them all out.
Stuck them together with contact adhesive *
* I checked first to see if it dissolved the polystyrene
as that could be a disaster but although it etched the
surface a bit, it seemed OK so I used it.
I trimmed the edges with a sharp blade to round them.**
** Sandpaper would probably be OK if you have some.
Finally I put some sticky backed plastic on the top to
make it more visually appealing. This is optional.
4 x Polystyrene Pizza tray
Contact adhesive - check if it dissolves the polystyrene.
If it does, use something else
optional - colourful sticky backed plastic
optional - sandpaper