bootstrap-reboot.css variables not defined in 5.1

[jaryn-kubik]

Looking at https://github.com/twbs/bootstrap/blob/fd92e353d078175074af35a94b7a237c64d6767a/dist/css/bootstrap-reboot.css for example body.font-family is defined using css variable var(--bs-body-font-family).

But these variables are not defined anywhere. Shouldn't bootstrap-reboot.scss also import _root.scss that defines these?
Maybe I'm missing something but including just bootstrap-reboot.css no longer works on it's own and it did before.

[ffoodd]

That's right, indeed. Using _reboot solely needs to import _root on its own.

FWIW we kind of already knew this, as it's been mentioned in #34577—simply missed the point.

[xiejay97]

@ffoodd I think provide a default value for css variables would be better.
As font-family: var(--#{$variable-prefix}body-font-family);, if we provide a default value just like this: font-family: var(--#{$variable-prefix}body-font-family, $font-family-base);, we wont need the --#{$variable-prefix}body-font-family variable, it means we can set css variables only when we need.