Fixed support for prefers-color-scheme

[JanBobolz]

Fixed support for browser's prefers-color-scheme (the previous attempts seemed to have no effect).

The precedence of how night mode is enabled/disabled is now as follows:

• If the user ever clicks a button, a cookie is set and that setting persists for 30 days.
• If the user never clicks any buttons, night mode is activated if any of the following happens:
  • the browser's prefers-color-scheme is dark.
  • the admin has set night mode as default.

So in particular, if there are no buttons and you don't set night mode as default, then the blog will now properly obey the iOS/macOS dark mode settings (dynamically, i.e. also if the page is already open when the OS switches dark mode on or off).

[John-S4]

Great commit - fixes the issue on Apple devices as stated and also on Windows and Android.

[dansleboby]

I confirm, using this fix enable the right behaviours, please merge it!