Okay. I think I see now.
For future reference, "Fandom" refers either to the company the runs the wiki farm or the farm as a whole. There are thousands of wikis each with their own templates. When asking how to use/copy a template, you should specify both the template and the wiki.
From what I can gather, you can copy the CSS if you want but it isn't critical to the main function of the template; it is just the default styling. As for the JS, it appears to be unused anyways so you should be fine not copying it. My guess is that the template used to use it but was later updated to use the standard Fandom collapse feature instead.