* v5: Simplify navbars by requiring containers

* Update migration docs for navbar

* Add variables for shades and tints of each major color

* getting-started/theming.md: use a `range`.

- Rename and move the variable to variables file
- Move code to the grid file
- Use the mixin to generate our own classes
- Wrap in a grid classes enabled conditional
- Document the mixin

* Allow .page-links to get left margin.

* Add border-radius to page-links in case they have left margin

* Apply MartijnCuppens suggestion to _pagination.scss

Co-Authored-By: Martijn Cuppens <martijn.cuppens@gmail.com>

* Plus if/else Rules

* Formatting fixes

* Fix border-radius for pagination-size

* Use mixin for default pagination sizing

- Remove unsupported browsers fixes
- More consistent comment blocks
- Reorganise order of some blocks
- Add height fix for date/month/week/time inputs (#18842)
- Remove redundant type selectors
- Additional resets and theming options for `legend`
- Add date & color inputs to reboot page
- Use the same borders for text search, text inputs, textareas and date inputs
- Move code styling to reboot

Drop `color()`, `theme-color()` & `gray()` functions  in favor of variables. The functions just called a `map-get()` of a map where just the variables were defined. 

Also the `theme-color-level()` now accepts any color you want instead of only `$theme-colors` colors. The first value now is a variable instead of the `$theme-colors` key.

* Use escape-svg() function

* Update theming.md

Also use `viewBox` instead of `viewbox`.

This was causing issues for RTL, see https://github.com/twbs/bootstrap/issues/28238

* 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...

- 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.