Open in kitematic and run the docker container. Click on the volume and allow access.
The volume must contain a file called server.py, which contains the basic web app (or includes it), the web app should be in this form:
from flask import Flask
app = Flask(name)
return "Hello, World!"
if name == 'main':
app.run(host='0.0.0.0', port=5000, debug=True)