Compiling issue in Manual with Sphinx

[JaeHyeokLee98]

at 94th line in docs/source/conf.py, the code
app.add_stylesheet('custom.css') should be changed to
app.add_css_file('custom.css')
The problem is caused by the version issue of Sphinx.
After Sphinx version 1.8.0, the API was deprecated. Please refer to this sphinx-doc/sphinx#7747

Also version error comes from sphinx-bibtex with error message : ExtensionError("You must configure the bibtex_bibfiles setting")
Using sphinxcontrib-bibtex version 1.0.0 can solve this issue and 2.0.0 makes this error. Please refer to this jupyter-book/jupyter-book#1137