Bokeh server and templates

How can I use a HTML template when I start Bokeh server as library within Tornado (https://bokeh.pydata.org/en/latest/docs/user_guide/server.html#embedding-bokeh-server-as-a-library)?

Concretely I use this (https://github.com/snowch/bokeh-cloud-foundry) example.

I embedded an index.html in the templates folder as in the examples on GitHub, but does not affect the web page in any way. Do I have to reference it?