[issue23951] Update devguide style to use a similar theme as Docs

[Roundup Robot]

Roundup Robot added the comment:

New changeset 9e7b1bc15ba7 by Victor Stinner in branch 'default':
Use the same style than Python ref doc
https://hg.python.org/devguide/rev/9e7b1bc15ba7

----------
nosy: +python-dev

_______________________________________
Python tracker <report at bugs.python.org>
<http://bugs.python.org/issue23951>
_______________________________________