bootstrap-reboot.css variables not defined in 5.1

Created by: 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.