title: Custom css file for jupyter notebook
body: <p>I would like to use custom .css style file for my jupyter notebook inside jupyterHub. I placed the <code>custom.css</code> file inside <code>~.jupyter/custom/custom.css</code> and <code>/opt/conda/lib/python3.6/site-packages/notebook/static/custom</code> and neither of them works. Any idea how to force custom css style when using DockerSpawner?</p>