from app import app
Ah yes, luckily I am currently developing a flask application at the moment.
You are currently missing the static folder which by default flask looks into, a folder structure something like this:
Hope that helps any questions just ask.
Plus - A good article to read but not super related but it talks about the folder structure of flask is this: https://www.digitalocean.com/community/tutorials/how-to-deploy-a-flask-application-on-an-ubuntu-vps