* Remove default kbd element shadow, simplify selector while here

* Add new -shadow-inset variable so our shadows match on .form-control's, .form-select's, and .progress's

* Reuse box-shadow variables for .dropdown's, .popover's, .toast's, .modal's, and .img-thumbnail's

* 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

* better way to do this contents stuff, redo the toc while i'm at it

* page restyle for docs while here

* un-callout that, edit text

* redo padding on toc

* fix toc

* start to cleanup checks docs

* Rewrite Markdown tables into HTML

* Redesign tables, redo their docs

* Replace Open Iconic icons with custom Bootstrap icons

* Redesign the docs navbar, add a subheader, redo the sidebar

* Redesign docs homepage a bit

* Simplify table style overrides for docs tables

* Simplify docs typography for page titles and reading line length

* Stub out icons page

* Part of sidebar update, remove migration from nav.yml

* Move toc CSS to separate partial

* Change appearance of overview page

* fix sidebar arrow direction

* Add footer to docs layout

* Update descriptions

* Drop the .form-group class for margin utilities

* Remove lingering form-group-margin-bottom var

* improve footer spacing

* add headings to range page

* uncomment form range css

* Rename .custom-range to .form-range

* Drop unused docs var

* Uncomment the comment

* Remove unused variable

* Fix radio image sizing

* Reboot update: reset horizontal ul and ol padding

* de-dupe IDs

* tweak toc styles

* nvm, fix dropdown versions stuff

* remove sidebar nav toggle for now

* broken html

* fix more broken html, move css

* scss linting

* comment out broken helper docs

* scope styles

* scope styles

* Fixes #25540 and fixes #26407 for v5 only

* Update sidebar once more

* Match new sidenav order

* fix syntax error

* Rename custom-file to form-file, update paths, update migration docs for previous changes in #28696

* rename back

* fix size and alignment

* rename that back too

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

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

Previously deprecated in v4.x, this clears out the now unused Sass option and removes some unused mixins. Arguably we could remove more, but I like the hover-focus mixin and we make extensive use of it across the project.

* Use $popover-border-radius

* Move and rename the local $offset-border-width to the global variable

- Line height & font family from html were directly overridden by body, so they were redundant thus removed
- The remaining properties are moved to body
- Shim for IE10 tags removed
- hr cleanup
  - Combined styles from reboot & type
  - Changed from borders to background
    - This allows us to keep the color inherited.
    - Opacity can be used to change the intensity
    - Size attribute will not change the height instead of making the hr look like an input field
  - Better variable names
- headings cleanup
  - Moved all element styling to reboot
  - Type will now extend the element styling. This way we will save some redundant code
- small & mark are also moved to reboot. type does not contain any element styling anymore
- font weight removed from small, this did not really made sense

Currently, `$toast-border-radius` uses the value of `.25rem`. This is inconsistent with other variables such as `$btn-border-radius` and `$input-border-radius`, which uses the "global" `$border-radius` variable.

- Drop hover and focus states
- Drop .badge-* variants and associated mixin for .bg-* utilities
- Drop .badge-pill for .rounded-pill utliity and adjust horizontal padding to find middle ground of .badge and old .badge-pill
- Remove unused variables
- Add default color value to .badge base class
- Update docs to reflect changes

* Add map-name param to _assert-starts-at-zero

* Set default value for backwards compatibility

In a scenario where `$input-line-height` or `$input-font-size` are different than `$input-btn-line-height` and `$input-btn-font-size` the final `$input-height-inner` was wrongly calculated.