We have incorporated everyone’s feedback in our latest release, announced here: Dash version 0.22.0 released!. It is now easy to add local CSS and JavaScript and we have provided an official way to override the Dash Index Template.
For more, read the official docs: https://dash.plot.ly/external-resources
If you have any particular questions about this, please create a new issue. Many thanks to everyone for their feedback on this issue 