Firefox

Flawless. Works so smoothly that I have forgotten I use it.

is dark reader regularly pinging home?

Super-interested in this! Dark reader is great, but there is a pretty substantial performance impact which is why I ultimately removed it.

Install Stylus > Write New Style > Import and then copy/paste this in. Keep in mind that I removed a lot of my specific tweaks for sites I use, because that's PII. You will encounter many more weird issues on random sites than you do with DarkReader, but if you're used to working with userCSS you'll probably have no issues fixing those. The way this essentially works is by inverting your entire browser screen, then rotating the hue so the colours of website themes aren't weird, then it inverts images back to normal. I'm sure there is a way to do this without inverting the images in the first place, but it would involve one hell of a lot more code than this. I wrote this originally in about 3 minutes.

html, iframe {
    filter: invert(1) hue-rotate(180deg);
}

img, div[background-image], div[style*="background-image"], video  {
    filter: invert(1) hue-rotate(180deg);
}

@-moz-document domain("lemmy.ml"), domain("ultimate-guitar.com"), domain("open.spotify.com"), domain("discord.com"), domain("localhost") {
/* Exemptions for sites that already have a dark mode */

html, iframe {
    filter: none;
}

img, div[background-image], div[style*="background-image"], video  {
    filter: none;
}
}

@-moz-document domain("youtube.com") {
#movie_player {
    filter: invert(1) hue-rotate(180deg);
}

video {
    filter: none;
}
}

@-moz-document url-prefix("https://www.google.com/maps") {
div[aria-label="Street View"] canvas, div[aria-label="Photo"] canvas, button[data-photo-index] {
    filter: invert(1) hue-rotate(180deg);
}

div[role="img"] {
    filter: none;
}
}

That sounds cool, I'm curious to try that!

Try Samsung Browser. It has a fantastic built in dark mode. I use it even on my non Samsung devices.

On mobile I don't think there's any other way, on desktop you can use the crude background/foreground color changer in the settings. I think only Chromium implemented an embedded dark mode as of today

@kratoz29
Is your Android phone on dark mode ? If so, Firefox will be on dark mode too.

If it's for the PDF, can't say, I don't think even Foxit Reader can transform PDF documents i'to dark mode ones on the fly (haven't tried on fact).
@QuazarOmega