Make index page single column

[kwankyu]

Part of #33833.

Compare

https://40377a6d73c60cf4aea16b1105d7b73ec96b11db--sagemath-tobias.netlify.app/reference/genindex-k

with previous

https://73e5aa3fbbec2d751a47064c14479fc0d55c3de9--sagemath-tobias.netlify.app/reference/genindex-k

Depends on #34252

Component: documentation

Author: Kwankyu Lee

Branch/Commit: 40377a6

Reviewer: Matthias Koeppe

Issue created by migration from https://trac.sagemath.org/ticket/34265

[kwankyu]

Branch: u/klee/make_single_column_index_page

[kwankyu]

Last 10 new commits:

f19b597	Add link to the logo
09d5f5c	Fix the logo link for reference
ae75d53	Fix a subtle reference problem for build_options
3519bed	Run docbuild workflow with single thread
1274718	Fix a suspicious part of categories doc
e5b1f7e	Add search.html
ebd3b77	Better pygments style
73e5aa3	Make white logo transparent to match with furo
183e558	Merge branch 'develop' into t/34252/revive-furo
40377a6	Make single column index page

[kwankyu]

Commit: 40377a6

[kwankyu]

Author: Kwankyu Lee

[kwankyu]

Dependencies: #34252

[kwankyu]

Description changed:

--- 
+++ 
@@ -1 +1 @@
-
+Part of #33833.

[kwankyu]

Description changed:

--- 
+++ 
@@ -1 +1,5 @@
 Part of #33833.
+
+Fix
+
+https://73e5aa3fbbec2d751a47064c14479fc0d55c3de9--sagemath-tobias.netlify.app/reference/genindex-k