Login into the Admin Panel using the provided credentials.
Click on the Settings icon from the left menu.
Click on Theme under the Appearance accordion.
On the Theme page, you’ll see two tabs – General and History. Click on the History tab.
Hover on the version name (e.g., 1.0.0). A three-dot menu should appear.
Click on Download in the context menu.
This will download a cms.zip file. Extract it under a folder named cms. Inside, you’ll find another folder named cms-<random>. That folder contains your base theme.