Change the documentation theme to Furo (#244)

The default one feels a bit outdated to me, let's try this[1].

I initially wanted to go with the RTD theme but it doesn't
support dark mode natively[2].

The theme is used in Python Developer's Guide[3] and it looks
nice in my opinion.

[1] https://github.com/pradyunsg/furo#elevator-pitch
[2] https://github.com/readthedocs/sphinx_rtd_theme/issues/224
[3] https://devguide.python.org/

docs/conf.py

@@ -94,7 +94,7 @@ pygments_style = 'sphinx'
 
 # The theme to use for HTML and HTML Help pages.  See the documentation for
 # a list of builtin themes.
-html_theme = 'default'
+html_theme = 'furo'
 
 # Theme options are theme-specific and customize the look and feel of a theme
 # further.  For a list of options available for each theme, see the
@@ -133,12 +133,6 @@ html_static_path = ['_static']
 # typographically correct entities.
 # html_use_smartypants = True
 
-# Custom sidebar templates, maps document names to template names.
-html_sidebars = {
-    'index': ('sidebar.html', 'sourcelink.html', 'searchbox.html'),
-    '**': ('localtoc.html', 'relations.html', 'sourcelink.html', 'searchbox.html'),
-}
-
 # Additional templates that should be rendered to pages, maps page names to
 # template names.
 # html_additional_pages = {}

requirements-docs.in

@@ -5,4 +5,5 @@
 #     pip install -r requirements-docs.in && pip freeze > requirements-docs.txt
 #
 # and then modifying the file manually to restrict black and mypy to CPython
+furo
 sphinx

requirements-docs.txt

@@ -1,8 +1,10 @@
 alabaster==0.7.13
 babel==2.14.0
+beautifulsoup4==4.12.3
 certifi==2024.7.4
 charset-normalizer==3.3.2
 docutils==0.20.1
+furo==2024.5.6
 idna==3.7
 imagesize==1.4.1
 importlib-metadata==7.0.0
@@ -13,7 +15,9 @@ pygments==2.17.2
 pytz==2023.3.post1
 requests==2.32.2
 snowballstemmer==2.2.0
+soupsieve==2.5
 sphinx==7.1.2
+sphinx-basic-ng==1.0.0b2
 sphinxcontrib-applehelp==1.0.4
 sphinxcontrib-devhelp==1.0.2
 sphinxcontrib-htmlhelp==2.0.1