Currently (as of 075ba86), the CSS referenced by the html is css_new/uswds.min.css. Normally, that would be built from the source file css_new/uswds.css. But it's not actually being minified in the build process. The minified file we're actually serving is committed to the repo, so it's static unless anyone manually updates it.

Heads up: this bug was very hard to find because the mapping between the source file and minified file (css_new/uswds.min.css.map) is also a static file committed to the repo. So looking in the browser's dev tools shows unminified css that won't match the actual unminified css you're editing.