By default, the web view uses a white background. This was causing an
ugly flash during the initial navigation to a page containing a web
view.
This was fixed by setting the web view's background to transparent in
https://github.com/ente-io/frame/pull/233/files.
That fixed the white flash. But when we use a transparent background,
it causesanother different sort of weirdness -- during the navigation,
the navigation bar remains visible, but the rest of the new screen
below remains transparent. So visually it looks as if only the
navigation bar is sliding in from the right.
The issue with fixing a color is that at some point, our web pages
will start having separate light/dark modes, and the background color
won't be fixed always. Currently though, we only have dark mode
pages. And also the app is only in dark mode, with a black
background. So using black as the background solves the navigation
weirdness, and also doesn't stray too much from the eventual color of
the rendered page.
