Thanks, merged manually.

👍 stylesheet needs to be added on the forum page too and i think that's all

I did it for the forum but it still sometimes flickers shortly when I press ctrl-f5 and have the bright theme enabled. Only seems to happen on the forum and only sometimes. Both in Firefox and Chrome.

Edit: Hmm, actually I also sometimes see it on ddnet.tw/status/

Yeah so i guess the more time it takes to load the page the more it might flickers, i still don't really get why it only happens sometimes.

I'm testing a few other possibilities if you have a look on http://krkrkr.org/ i'm now loading the css using js only, and that js is a the top of the default layout, so the browser is only downloading one css file each time ( i copied the halloween theme at the bottom of the normal theme ).

Even when i'm doing it that way i can still see some flicker even tho it's a different type of flicker like the svg logo can appears on the page briefly then the theme is loaded, i don't get how that's possible 'cause the browser is supposed to load the css before the logo. (inline js like it's on the demo atm is supposed to stop the parsing of the index, execute that js then continue parsing/loading the page, obviously the page is getting parsed while the js is executing or something)
I'm not familiar at all with js i'm mainly used to C so it's possible that i missed something i don't know.

Doing it serverside seems to be a solution but i don't like this idea so i'll keep digging !

edit: seems to appear more on firefox strangely
I'd like to know if the flickering on krkrkr.org is more pronounced for you ? For me it seems to be less pronounced on chrome and kinda more pronounced on firefox

Nono, only rendering it with js is no good. DDNet.tw should keep working without js. I think I'll try doing it serverside with nginx like this: https://stackoverflow.com/questions/26128412/how-to-extract-some-value-from-cookie-in-nginx

So that it redirects the css based on the cookie that's set. Then the JS is only responsible for switching the cookie and reloading live.

Yeah you could get away with using js for it because there's a "noscript" html tag, everything inside that would be executed by a browser only if it not using js, i did not test that but as i said even with that technique i still get a different kind of flickering.

Indeed being able to do that part directly withing nginx seems doable, still would involve like two "path /..." and like return 404 if cookie value is X for this path. Way better than doing it in php or something which is what i meant by doing it serverside.

        location /css-halloween.css {
		if ($http_cookie ~* "user_theme=/css-halloween.css") {
			return 302 /css/css-halloween.css;
		}
        }

works great for me, just mv'd the halloween theme into a "css" folder, js needs code removal and tweak to reload page when switch is switched on

Nice!

Here is the updated themes.js : https://ptpb.pw/_9XM
( no more enable_available_css & added a page refresh when halloween theme is selected using the switch )
I assume i don't need to PR for that ?

The other files don't need changes, just moving/renaming the "css-halloween.css" file and put it's new location/name in the return 302 statement in nginx.

Did not test with ssl, i'm sure your nginx conf is a bit more complicated so on like you might have to put twice this rule for the website & the forum.
Might need a ctrl+f5 to clear browser cache but as it is on http://krkrkr.org/ that works like a charm !

Works perfectly! I also added a return 302 /css/css-empty.css for the else-case. Don't need duplication, nginx has include files.

(Generally If in nginx doesn't work properly, but in this case it's fine: https://www.nginx.com/resources/wiki/start/topics/depth/ifisevil/)

Awesome ! not the best method if you ever have to easily change theme or something but way better than that flickering 👍