Feature Request: Define initial value for "dark mode"

[certara-mtalley]

Apologies if this exists in some capacity, but I have yet to find a simple way to do this or an example of someone else doing this with the new dark mode functionality.

It'd be nice if the YAML for a pkgdown site could explicitly define the dark mode setting it will load with; dark, light, auto. Currently its just light-switch: true.

When running on Chrome & Edge in Windows 11, pkgdown pages load either "light" or "dark" depending on what my systems display settings are (which if this is the default behavior, why not just default to "auto"?). Sites also seem to remember previous settings and load with the last selection. If a page loads on "light", and is changed to "dark" and the page is closed, opening it again will cause it to load "dark". This seems fine, but my selections on someone else's pkgdown site (bslib for example) will also control how my own personal pkgdowns display.

Ideally, I'd like all pkgdown sites for my users to load in "light" mode, regardless of their system settings or any toggling they may have done in another window. If this ability does exist internally, maybe bring attention to it in the customise vignette?