Third-party assets in the preserved 3D tutorial

Sphinx stylesheet assets
Copyright 2007-2011 by the Sphinx team.
The original stylesheet copyright notices are retained. See Sphinx-LICENSE.txt
and Sphinx-AUTHORS.txt, supplied from the historical Sphinx 1.1.3 distribution:
https://pypi.org/project/Sphinx/1.1.3/
Local change: removed the reference to an unavailable search-result icon.

SHJS syntax highlighting
Copyright (C) 2007, 2008 gnombat@users.sourceforge.net.
Distributed under GNU GPL version 3. See SHJS-GPL-3.0.txt.
Readable source is included as sh_main.js, sh_javascript.js, and sh_html.js,
alongside the original .min.js copies. Sources and language-generation tools:
https://shjs.sourceforge.net/doc/download.html

Illustrations credited in the tutorial retain their original attributions.