This sub-theme requires the full USWDS assets folder.
style.css for this theme includes some example code items related to expanding the theme out to full page and also a fix for USWDS small form width.
Go to https://github.com/uswds/uswds#download
Follow the directions on downloading the USWDS tar.gz file from the latest USWDS release and open that file.
In the subtheme, the libraries.yml file is looking for the USWDS files in package/dist/