- Updates the utilities mixin to check for specific CSS variable names via `css-variable`
- Bonus fix: we now prevent local variables for `0` value utilities (e.g., `.border-top-0` no longer sets `--bs-border-opacity: 1`
- Adds new `.border-opacity-*` classes
- Adds new root variables: `--bs-border-color`, `--bs-border-style`, `--bs-border-width`
- Documents the new variable changes
* Disabled link cleanup
per https://www.w3.org/TR/html-aria/#docconformance
> It is NOT RECOMMENDED to use `aria-disabled="true"` on an `a` element with an `href` attribute.
>
>NOTE
>If a link needs to be "disabled", remove the `href` attribute.
This PR removes the unnecessary `href="#"`, `tabindex="-1"`, and `aria-disabled="true"` from disabled links in both docs pages and examples. `aria-disabled="true"` *is* kept for disabled link-based buttons (that have `role="button"`) as there it's appropriate to use (you *want* to convey to assistive technologies that this thing you're claiming is a button is also disabled at the moment)
Further, the PR extends the "Link functionality caveat" to show the "proper" way (removing `href` and adding `.disabled` class only) to disable a link, but then explains what to do if that's not possible (and then keeps an example with all the traditional `href="#" tabindex="-1" aria-disabled="true"`, but explains clearly that it's not ideal). Same sort of explanation is also added to the pointer event utilities page
* Turn big note into actual normal doc text
Co-authored-by: Mark Otto <markd.otto@gmail.com>
Co-authored-by: Mark Otto <markd.otto@gmail.com>
Co-authored-by: XhmikosR <xhmikosr@gmail.com>
