doc: update the documentation generator to match the new website

Signed-off-by: db0 <db0company@gmail.com>
Signed-off-by: Clément Bœsch <u@pkh.me>
doc: restore default.css

This partially reverts 9ce64ba111221a37bdd78204b67330a6120f6c50.

FATE still needs it until its design is updated to the new website
version.
hevc: fix offset for sao temporary frame

fixes fate on alpha

cherry picked from commit 0a8ce1cbdaff7cd026bcf95ee3787bc7b4c063ee

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>