Splash screen should be dark in dark mode

[Booligoosh]

I don't think there's a way to do it based on what's set in the app, but apparently this works based on the system dark mode:

GoogleChrome/lighthouse#3891 (comment)

It wouldn't really look that out of place if it launched with a dark background when the system is dark but the app is light or vice versa.

[Booligoosh]

Update: This doesn't appear to work, it just shows the background as pure black regardless of the system theme. Not sure that this is fixable until there's a way to specify different background colors for different themes in the manifest.