Yeah, that's a very good question. It will be much helpful if the OP shares the link here. So that all of them members can visit and leave helpful replies. 

Sorry that turned out rather more difficult than I thought it might be. Is there some how to guide I missed?
Anyway, now that I've got some time to have a look at this again. I'm rather glad I started early... I've uploaded what I've done so far if someone wants to have a look: mega.nz/file/VpBXBapK#9c5Lphxa43pSl1y2oz...AHTga0pzL_rTRJKhnLW0

That said, I'm not sure if the .css file is affecting what's being shown at all. Since even changing stuff in working styles doesn't seem to affect what's shown in limesurvey. If I change the coloration of the answers, there's no effect.

If I literally delete the entire file and save, there's no effect. I'm honestly baffled why that is. I deleted the entire cache of my secondary browser thrice, trying this in different configurations without any effect.

It's almost like it's saved the cardsort.css once in my databank and is using that backup, rather than getting it from the upload folder. Could that have happened? Do I need to force reupload this somehow?

I asked for a link to a live survey so I could see the source.

Someone on the discord told me a solution. Apparently something was cached somewhere (but not in the browser), which prevented it from using the new version.

You can solve that by altering the config.php in limesurvey/application/config/config.php. You need to set debug = 2 (or in my case debug=>2). That apparently makes it reloaded cached data. This worked for me.

So with the cacheing issue overcome I've made some rapid progress.

This basically works, but is kinda ugly and requires survey users not to be idiots. So yeah suboptimal. But that's as far as I can get with twig and css, I think.

As the next step I want to just have one answer that replicates column number times. And I also want to check if the answer was already given in the column, in which case I want to remove the previous answer (or just reject the new one depending what works better).

So I need to get started with the java script. I've just got two issues there. I need to read the colum names out of either the twig or from the server (and I have no clue how to access either).

And I need to see on which class (items-end-wrapper) - identifiable by its column label - the answer got dropped. I figured for this I'll just need to check if the column label was already used for the variable/answer. Sorry if I horribly mangled java syntax here. I'm only really familiar with C#, so no clue if this is possible at all or what steps are required to make it happen. For example: I think the colLabel class I'm defining in my twig that contains my colum labels, doesn't actually hold them but is just printing them ("ind" is the label here).
So do I need to define some seperate java class for this, is this twig enough so I can access the information from the js, or can I make the "ind" information otherwise readable from the js?