While #28450 overhauled a ton of forms work, the  support for this custom file input was ineffective. This updates the selector to target the custom field and gray out the entire field.

Fixes #28176.

The previous link is dead one.

Media queries do not support CSS custom properties (CSS variables), so we've had some useless variables lying around since shipping v4. This finally removes them and the associated documentation content that explained the situation.

Fixes #29012.

Corrected minor spelling error.

* Initial spike of consolidated form checks

* Stub out forms rearrangement

- Prepping to drop non-custom file and range inputs
- Prepping to merge custom and native checks and radios (with switches)
- Prepping to merge custom select with form select
- Moving docs arround so forms has it's own area given volume of CSS

* Move input group Sass file to forms subdir

* Start to split and move the docs around

* Simpler imports

* Copyediting

* delete overview file

* Remove commented out code

* remove the custom-forms import

* rewrite flex-check as form-check, replace all custom properties

* Remove old forms doc

* stub out new subpage link section

* update migration guide

* Update nav, forms overview in page nav, and descriptions

* fix check bg position

* fix margin-top calculation

* rename .custom-select to .form-select

* Update validation styles for new checks

* add some vertical margin, fix inline checks

* fix docs examples...

* Revert "Fix readonly-plain-text with button addon (#25871)"

This reverts commit ff40e003.

* Add migration comment

x-ref #28987

Pagination used to have box shadow back in the days which required this property, but nowadays it's redundant. (see https://github.com/twbs/bootstrap/blame/0cd186183c5e18f0517d6037d53f29c56adbac72/less/pagination.less#L17)

- Remove IE10 background hack
- Ability to change the pseudo element
- Ability to change the z-index
- Remove pointer events, just inherit this

Add unit test from #28912 to v5

To fix RGBA borders overlapping issue.

fixes issue #28892

The cross icon was confusing since some browsers use it as a reset button.

Just firing the focus event isn't enough ... need to actually call the proper `focus()` method for it to actually do it...

* Add Error checking to prevent invalid breakpoint

Error checking to prevent invalid breakpoint name

* check type rather than value

* Revert "check type rather than value"

This reverts commit 04ab1e65.

* use of not rather than null

Co-Authored-By: Shohei Yoshida <fellows3@gmail.com>

Co-Authored-By: Shohei Yoshida <fellows3@gmail.com>

* Remove unused classes/styles and use utilities instead of specific styles
* Use `getElementById` instead of `querySelector`

- Add same advice about keyboard/AT handling to popovers as a callout; also add information about not adding excessive content or interactive controls (and the suggestion to opt for a modal)
- Tweak the tooltips callout for consistency