Many browsers on mobile especially on android don't have dark mode and for some the dark mode is pretty messed up. Chrome for example is a very common and popular browser on mobile and it doesn't have a very responsive dark mode. Fun thing is I for some reason just prefer this forum in light theme.
What are you still doing with chrome? Use Firefox for android and install Dark reader. You will thank me later 
I've also used Microsoft Edge on my IOS device to achieve the Dark mode option on the forum without much stress. It took me less than 30 seconds to navigate with just about three to four steps to activate. If anyone, for any other reason, prefers using Microsoft Edge over the Firefox or already have Microsoft Edge as their default browser, they can use the Microsoft Edge app, too.
Let me assist with screenshots of the simple steps:
- Go to 'Settings'
- Click on 'Appearance'
- Check Advanced Appearance Setting tab and toggle on the 'Dark theme for all web pages' option
And that's all.
This interface is very okay to me plus the signatures and avatars are clearly shown and structured on the website. The advantage is that it reduces the light penetrating one's eye to a more healthy view with less light intensity.
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Infact I think this is the longest place I surf on light mode because I use dark mode most of the time outside the forum, well I guess photochromic glasses cover for that.
Even the default night light filters for Windows and Linux can be very helpful. I can spend so many hours on PC with the blue light filter on. I can't spend more than 10 minutes on my PC minus my eyes hurting when I turn it off.It is best adviced to not take the health of the eye for granted, why I will recommend Dark mode for myself is to protect my eyes from any light effect especially as we spend a whole lots of screen time overnight without wearing glasses. Many people neglect this until they begin to experience one itches and red eyes.
You have to make your own version of dark theme switch because there was never any work done on official SMF forum dark theme.
There are plenty of options you can use depending on browser and device you are using.
If you want to apply dark theme to all websites including bitcointalk than Dark Reader extension is a good option.
There are plenty of options you can use depending on browser and device you are using.
If you want to apply dark theme to all websites including bitcointalk than Dark Reader extension is a good option.
While I think it is possible for bitcointalk forum website to be programmed to have the feature of dark mode either at the header or footer position of the site but, it might not be necessary since the website already works smoothly with the light or dark mode of the browser settings.