Does Safari have a night mode? Most of my work at night is either in Mail (which should be relatively easy to enable night mode on) or a web browser. Obviously, third-party browsers will have to decide whether to support night mode, but I wonder if Safari will have support when Mojave is released.

I imagine it won't be trivial to do this, especially on pages that have a background image. You don't want to invert it, but leaving it as-is would ruin the night mode effect. Plus, you have to maintain sufficient contrast with foreground text.