This is your Nim codebase — like a VS Code working folder, stored in your browser (IndexedDB). Click a file to edit it. The whole folder is mounted at /workspace on every compile, so import sibling and import sub/mod work. Run compiles the file open in the editor; Build compiles main.nim into the Site folder.

This is the deployed static website — the working folder of the app pane, which renders this folder's index.html. Press Build to compile your project into it (app.wasm + index.html + the runtime). You can add your own files (CSS, images, …) — Build only overwrites app.wasm, nim-runtime/* and a generated index.html.