Yes, you can use BSS however you like.
I’m just trying to be helpful. I’ve owned a graphic design company since 1993. I started out doing typesetting and artwork for printers back when we shot camera ready art with actual film, and used ruby-lith to block out text. I’ve have owned and used dozens of computers and dozens of programs, from Final Writer and Pagestream on the Amiga, to Quark Xpress and Pagemaker on the Mac, to MS Word, Corel and InDesign on the PC. I’ve done everything from typesetting a single word, to writing, illustrating and editing full-blown novels. Most of the time, I had no choice in the colors of the software (i.e. "dark-mode, light mode) This is a relatively recent development (although the Amiga did allow you to do virtually anything in terms of workspace customization, but that computer was 10 years ahead of its time.)
Point being, this was my vocation for 25 years. I didn’t mean to sound insulting with the “absurd” comment, but as someone who’s done this for a living for most of my life, I can tell you that unless you’re specifically going to publish this novel on the web, and ONLY the web, then writing a novel in a website builder is like trying to build a house using the heel of your boot as a hammer. If you have absolutely no other option, I suppose you’ll eventually get it done, but wouldn’t it be a lot easier to just get the right tool for the job?
I don’t know what computer or O.S. you’re on (this makes a big difference), but the problem is that modern word processing software that gives you the freedom to alter the UI is not inexpensive, and getting older programs to run reliably on Window 10 is always a crap shoot. That’s one reason why I continue to use Window 7, Adobe Creative Suite, and have refused to upgrade to Windows 10. Eventually, those of us on Windows machines will have no choice but to upgrade to 10, and then be forced to upgrade to cloud-based/subscription-based software, since that’s where he entire computing world is moving towards and all the big companies are in cahoots in this regard. You cannot use the latest Adobe Creative Cloud software on Window 7, and you can’t run the older Adobe Create Suite software on Windows 10 (at least not easily.)
These software leviathans want the entire world to be on monthly payment plans for everything. It’s nauseating.