Custom notebook logo

[Rusi Mody]

I followed http://sherifsoliman.com/2016/01/11/theming-ipython-jupyter-notebook/
and by copying the file into .jupyter/custom/custom.css the colors changed

Now if want to make a custom notebook, let us say, with a custom logo, where should it go?
In particular where does the jupyter logo come from?

$ jupyter --version
4.2.1