If you follow the plot.ly Dash tutorial, you’ll find that it will run locally and no internet connection is required.
Follow tutorial to create a simple app, run it locally through your terminal, put in the default local host ip and port (http://127.0.0.1:8050/) in any browser and voilá.
You have publish your app on something like Heroku or a server in order for your work to be accessible for outsiders.
Here is a link to the tutorial:
https://dash.plot.ly/getting-started