Documentation CSS doesn't work on Firefox dark theme

[darksylinc]

See https://forums.ogre3d.org/viewtopic.php?p=554699#p554699

In Firefox about:preferences one can set the Dark Theme.

• https://ogrecave.github.io/ogre-next/api/latest/ is unredable
• https://ogrecave.github.io/ogre-next/api/2.3/ works fine

The community seems to have tracked the problem to https://github.com/OGRECave/ogre-next/commit/e712f532fcd1b6572ac2ca46357f75b18d086f51 but further research is needed.

[darksylinc]

The problem has been fixed.

There were two changes now:

• I switched to another CSS theme (awesome doxygen).
• The CI script we were using was not overwriting all the files, thus old and new CSS were getting mixed. Fixed by switching to doing it ourselves.