HI Big Picture,
I think you're looking in the wrong place to solve your problem. It is a default feature of Moodle to force users to log in to the LMS and show a login page that has no top bar in Boost.
There's no need to hack in any code or change an SCSS preset. Instead, give this a go:
- Open Site administration > Security > Site security settings and look for the setting labeled 'Force users to log in'.
- Tick the box and save settings
- Check in another browser to see what the result is when going to your LMS's main URL.
You'll see the user has no other option than to log in, and that there's no top bar on that log in page.
If you're unsure about this, have a look at the corresponding Moodle Docs: https://docs.moodle.org/36/en/Site_security_settings#Force_users_to_login