Jesus Canadian Christ! It finally worked for the backgrounds!!!
Okay, so after doing what you told me, I got it to work but it wouldn't save and would reset when I closed it, so I just opened the Sources tab after changing the colors and copying the code and pasting it into the .css file and it worked.
document.querySelectorAll(`#main .ace_content`)
was helpful with editing the program colors (body, header, scroll bar, etc.), but I can't seem to find results that point me towards editing local variables, strings, functions, and so on. Any further step (or different one) you can give me? I'm finally so close to the finish line with this!
Edit: I forgot to mention, I typed aceEditor.debugShowToken() in the Console tab and it didn't yield any results for me (says undefined).
Thanks YAL, this was really helpful. I understand YT vids are a hassle to make, so I would highly encourage you to make a text based tutorial with GIFs whenever your busy schedule allows it, as a lot of people would get overwhelmed in this easily. After a few weeks I'm still not done editing the whole layout on my end.