In more detail
Themescape keeps no copy of your project, on its servers or in your browser. When you have refined definitions, starred favourites, marked connections or arranged the map, you save that work as files on your own computer. Loading the same files next time carries on where you left off.
A save downloads the four files the template uses, Data, Framework, Connections and Settings, plus a layout file when you have arranged or built anything. Each is named after your project, with "themescape session end" and the date and time added.
In Themescape
Choose Export, then Your progress, or Exit with my progress in the Log out box. On Start a project, add the files to their slots; file names decide which slot each one fills. If you close the tab without saving, changes since your last save are gone.