Special handling in javascript and css for any image whose `alt` value starts with `Logo`, rather than targeting one specific value.
Remove 2 no-longer relevant statements from `extra.css`.
Add css member for `mkdocs` theme.
Add link to PhpSpreadsheet site to the bottom line of each page for `readthedocs` and `mkdocs` themes. In theory, these links should already exist, and they do locally, but not, for some reason, when run on readthedocs.io. This link is different from the `Edit on Github` link at the top, which is a kind of interesting feature.
Add a bookmarklet on the main page for toggling images to dark mode, which would probably be the preference for users employing dark mode. Images are usually left unchanged in dark mode, but almost all our images are screenshots, and dark mode might be appropriate for them.
Use a white, rather than transparent, background for logo, making it viewable in dark mode.
A bit better emulation of dark mode in the readthedocs theme, which does not handle it "naturally".
oleibman