I was confused by this too, but you have to load the sample zip before opening the UI - the "filesystem" in the editor isn't a real one (as far as I can see) bu

I was confused by this too, but you have to load the sample zip before opening the UI - the "filesystem" in the editor isn't a real one (as far as I can see) but a virtual one in the browse that's saved in some kind of persistent storage.