levin192

Make breakpoint CSS variables available when not using _grid.scss

2

### Prerequisites - [x] I have [searched](https://github.com/twbs/bootstrap/issues?utf8=%E2%9C%93&q=is%3Aissue) for duplicate or closed feature requests - [x] I have read the [contributing guidelines](https://github.com/twbs/bootstrap/blob/main/.github/CONTRIBUTING.md) ### Proposal Bootstrap’s breakpoint CSS variables (e.g., `--bs-breakpoint-md`) should...