[twine2][sugarcube2] disable/replace default css/html

'lo all.

i'm building an rpg interface, and need to divided it up into sections like #map, #text, #actions, etc. My theory is this would be a lot easier if I just completely replace the default html and css and build anew. I wanna set up each section as a small passage and then load them into the section, like some kind of table, and then be able to address the section content like #map.$foo = bar

Problem is my programming experience is all, y'know, programming not web dev. So a few questions for y'all:

1) How does one disable or completely replace the default css/html?
2) How does one make a page element outside the normal #passage and address it?
3) unrelated, but can you change your default text editor? i'd rather use n++

thanks lovelies.