Created attachment 389165 [details]
Screenshot demonstrating bug
Since r255342, we attempt to use only the light GTK theme for rendering in the web process.
However, we fail when displaying the first two of these simple test cases:
Screenshot of the first test page attached. The page background should be light, not dark.
It's caused by EphyWebView's style_updated_cb(). Ephy will need to stop setting its own background color.
Removing this call from Epiphany reintroduces https://gitlab.gnome.org/GNOME/epiphany/issues/960. We need WebKit to use the UI process background color as its default background color temporarily, just until web content loads, but not longer than that....