Update documentation images to use the 4.6 'Modern' theme

[RespiteFromReality]

I'm interested in contributing updated images with the new passivestar theme for the docs (and contrib docs), but wanted to know a few things first:

1. Is there even interest in me doing this rn?
2. Is the theme still getting any major changes?
3. Is anyone already working on this? (didn't find an issue)
4. To what degree should this be split up.