https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64257
--- Comment #6 from David Malcolm <dmalcolm at gcc dot gnu.org> --- "pyramid" theme was added in: https://github.com/sphinx-doc/sphinx/commit/442229dd97160535e388473760002c1f1c495bf8 which appears to be in sphinx 1.1 onwards.
