Sometimes, I read a lot of stuff on this forum. I prefer to have the dark theme set-on.
Most of the time though, I read for about a few minutes, and then realise it was white, effectively bothering my eyes. So, that's when I usually decide to change the theme to dark, once and for all.
Needless to say, everytime I do the action the site brings me back to the forum's main page.
Really annoying, as I need to access the page itself once again, and they're usually not accessible in 2 mouse-clicks.
So incidentally, the suggestion to this problem would be to make you stay on the page, when switching theme.
So that you don't lose time, and can immediately concentrate on the thing you're doing (Namely for me, reading), instead of being forced to think of something else that's pointless (Namely, having to load the page again)
On a side-quest, it would be good if the choosen theme would be saved, at all time.
That would be convenient if per example, I do login on my account, and the theme is dark since last time it was the same. It can be annoying to always switch it back...Or maybe, that's just because I'm a lazy person. But still !
Although I don't know anything about coding, that's how I would imagine it to work :
So for each account on this site, you have a variable that keeps track of the used theme.
Namely, 0 for white and 1 for dark.
When you login, the site will read that value, and then switch to the lastly used theme, just for you.