It seems that the generated project already has lots of colour variables like --bs-body-bg. Dev.tools say it is in _root.scss, but that file does not seem to exist, and I suspect it is inside of bootstrap.in.css. Can I customise those existing colour variables?
>Solution :
It’s coming from scss.
You should have other _XXX.scss. SCSS compiler will make a global CSS file for the whole project. Dev tools present you the origin _root.scss not the compiled CSS.
Find the big CSS file of your project, you will find your variables.
If you know scss and have access to the whole tree of scss and all the files, you can rebuild the global CSS in house.
Other way, you make another CSS file, you put it after the global CSS, and you override definition you need… Not the smartest, but if only some changes to do lot quicker.