I’m also having the same issue, but I’m not sure why.
I do believe that the app.use() needs to be above the app.get() since Express looks at the routes at the top first, but I have my code ordered that way and it’s still not picking up the style.css
EDIT:
I got my solution to work by clicking the ‘open in new tab’ button in the preview window. That pulled in the CSS and solved the challenge.