Trac #33833: Make furo sage standard doc theme

In #33601, the furo theme has been introduced for the documentation. The
aim of this ticket is to make it the standard theme. Before it happens,
the remaining issues need to be fixed:

- Index page in double columns look awful -- fixed in #34265
- sage logo in the side bar should link to the top of the Sage manuals -
fixed in #34252
- no link to the doc root - fixed in #34267
- search page not working - fixed in #34252
- "ERROR: Adding a table of contents in Furo-based documentation is
unnecessary" - https://73e5aa3fbbec2d751a47064c14479fc0d55c3de9
--sagemath-tobias.netlify.app/installation/source.html#installation-in-a
-multiuser-environment - fixed in #34262

To support this ticket, the standard Furo package was accepted by the
voting done in

- https://groups.google.com/g/sage-devel/c/VTU_I-ecPlA

along with subsidiary votings in

- https://groups.google.com/g/sage-devel/c/eRh16v5Mz0c
- https://groups.google.com/g/sage-devel/c/rhPECxe128o

Other possible improvements:

- Install sphinx-hoverxref, sphinx-notfound-page (see setuptools
documentation, which also uses furo -
https://setuptools.pypa.io/en/latest/history.html#documentation-changes)

URL: https://trac.sagemath.org/33833
Reported by: gh-tobiasdiez
Ticket author(s): Kwankyu Lee, Matthias Koeppe
Reviewer(s): Matthias Koeppe, Kwankyu Lee

Author: Release Manager

.github/workflows/doc-build.yml

@@ -24,7 +24,6 @@ jobs:
           # Reuse built SAGE_LOCAL contained in the Docker image
           ./bootstrap
           ./configure --enable-build-as-root --prefix=/sage/local --with-sage-venv --enable-download-from-upstream-url
-          make furo
 
       - name: Build
         run: make doc-html

build/pkgs/configure/checksums.ini

@@ -1,4 +1,4 @@
 tarball=configure-VERSION.tar.gz
-sha1=c44fe4052d0d6ba38b7e60b82fa757fe40290433
-md5=bd8ae7f5adee5ff7baea95f143c5f857
-cksum=371288794
+sha1=23560f10767addedb5a1427d8d5edaf01ef1f31c
+md5=ff94d32b21e117d264e4cf5ba47834f0
+cksum=4110255875

build/pkgs/configure/package-version.txt

@@ -1 +1 @@
-6da95c029d7e1c153af30f8f2f19396efcf7e199
+fcc25ebf82c72cfe50e2b305deb55595e1537de8

build/pkgs/furo/type

@@ -1 +1 @@
-optional
+standard

build/pkgs/sagemath_doc_html/dependencies

@@ -1,4 +1,4 @@
-sagelib sphinx pplpy_doc | $(SAGERUNTIME) maxima networkx scipy sympy matplotlib pillow mathjax mpmath ipykernel jupyter_client conway_polynomials tachyon jmol ipywidgets jupyter_sphinx sage_docbuild elliptic_curves
+sagelib sphinx pplpy_doc | $(SAGERUNTIME) maxima networkx scipy sympy matplotlib pillow mathjax mpmath ipykernel jupyter_client conway_polynomials tachyon jmol ipywidgets jupyter_sphinx sage_docbuild elliptic_curves furo
 
 # Building the documentation has many dependencies, because all
 # documented modules are imported and because we use matplotlib to

configure.ac

@@ -489,7 +489,7 @@ AC_ARG_ENABLE([doc],
   AS_HELP_STRING([--disable-doc],
                  [disable build of the Sage documentation and packages depending on it]), [
     dnl Disable packages needed for docbuilding
-    for pkg in sage_docbuild alabaster babel snowballstemmer imagesize sphinx sphinxcontrib_devhelp sphinxcontrib_jsmath sphinxcontrib_serializinghtml sphinxcontrib_applehelp sphinxcontrib_htmlhelp sphinxcontrib_qthelp sphinxcontrib_websupport jupyter_sphinx; do
+    for pkg in sage_docbuild alabaster babel snowballstemmer imagesize sphinx sphinxcontrib_devhelp sphinxcontrib_jsmath sphinxcontrib_serializinghtml sphinxcontrib_applehelp sphinxcontrib_htmlhelp sphinxcontrib_qthelp sphinxcontrib_websupport jupyter_sphinx furo; do
       AS_VAR_SET([SAGE_ENABLE_$pkg], [$enableval])
     done
     AS_VAR_IF([enableval], [no], [dnl Disable the docbuild by disabling the install tree for documentation

src/doc/common/static/custom-furo.css

@@ -2,3 +2,12 @@ span.sidebar-brand-text {
   font-size: small;
   text-align: center;
 }
+
+div.highlight {
+  background: #F4F4F4;
+}
+
+body[data-theme="dark"] div.highlight {
+  background: #383838;
+}
+

src/sage_docbuild/conf.py

@@ -260,15 +260,15 @@ def set_intersphinx_mappings(app, config):
 
     # The name of the Pygments (syntax highlighting) style to use. This
     # overrides a HTML theme's corresponding setting.
-    pygments_style = "tango"
+    pygments_style = "sphinx"
     pygments_dark_style = "monokai"
 
     # Add siderbar/home.html to the default sidebar.
     html_sidebars = {
         "**": [
+            "sidebar/scroll-start.html",
             "sidebar/brand.html",
             "sidebar/search.html",
-            "sidebar/scroll-start.html",
             "sidebar/home.html",
             "sidebar/navigation.html",
             "sidebar/ethical-ads.html",