Options for testing MW site configuration, js, css?

Is there a sandbox wiki that I could use to test various admin-configurable options on, including js and css styles? Or a way to spin up a temporary sandbox wiki for that purpose? Something with a button that makes it easy to reset to default would be handy. Currently I would just install a wiki on my own machine; but I've done that often enough that it occurs to me it would be a useful service for other testers.

In a personal machine, you can create a normal account and an admin one.

In public wikis, this could help admins to manage ponctual rights for regular users able to become step by step admins.