* style: `_variables.scss` comments consistency

* style: `_variables.scss` spacing consistency

Blockquote footer font size is currently hardcoded to 80%, implying (in a comment) that this would result in the default font size. However, since the blockquote font size itself is variable, this is not necessarily true, and 80% of anything actually results in an arbitrary font size.

80% as a default is still fine.

fixes #26476

* add 'lighter' and 'bolder' font weight classes

these are 2 special values for font weight, that will give their content a font-weight value of 100 more or less than their inherited font-weight.

probably doesn't fully fulfill this issue, https://github.com/twbs/bootstrap/issues/23969, but it's a start

* Update .stylelintrc

* add 'lighter' and 'bolder' variables per @mdo 's request.

Fixes #26227

* Fix focus box shadow of custom ranges

* Put `:focus` selector right after `.custom-range`
* Remove unnecessary `outline: none`

* Fix box-shadow issues in IE/Edge

* Better align

* Fix thumb vertical positions in IE/Edge

* Fix incorrect formula of thumb vertical positions in Webkit

* Fix an incorrect comment

* Fix incorrect box-shadow-width

- Only applies to textual inputs and textareas with `.form-control` and selects with `.custom-select`
- Wrap the feedback icons in a Sass variable option, $enable-validation-icons, so folks who theme can disable
- Update docs to summarize styles, mention the icons, include a textarea demo, and add mention of the Sass variable option to the Theming section

- Fixes #25656 where custom selects had the wrong focus shadow
- Fixes #26668 where custom selects had no inset shadow (also closes #26572 which had the wrong form classes on the first example anyway)

Pagination move `.page-link:focus` outline value to variable `$pagination-focus-outline` so we can unset it via Sass and don't have to re-implement browser defaults

* Allow url(), attr(), none,... as breadcrumb divider
* Update breadcrumb divider docs

* added the styling

* added the documentation

* update for one rule per line

* fix hound error: trailing whitespace

* trimmed off vendor prefixes

* Add note about track and thumb

* Psuedo-elements must be split across multiple rulesets to have an affect

* Fix firefox inner focus

* Seems that FF is the only one affected by this

* Add support for gradients

* Add labels, clarify min/max changes

* add step example

* add custom range vars

* set color to `.form-control-plaintext`
* fixes readability on dark themes like ‘darkly’
  * https://bootswatch.com/darkly/index.html#forms
  * https://bootswatch.com/slate/index.html#forms
  * https://bootswatch.com/superhero/index.html#superhero
  * https://bootswatch.com/solar/index.html#forms

/cc @thomaspark

* use $input-bg for $custom-select-bg

Currently bootstrap only provides 4 variations of `width` and `height` css utilities, which are:

1. 25%
2. 50%
3. 75%
4. 100%.

Here, I'm adding `auto` to the list. This is useful when we need to reset the width/height value
back to the browser default value at some point.

When changing `$input-border-width`, `$input-height-border` does not change and `select.form-control` `custom-select` `custom-file` will still have `$input-height` which is resolved from `$input-btn-border-width`

This will work in cases when want controls with border, and buttons without.

Temporary fix will be to override 2 variables

```
$input-border-width: 2px !default;

// which is
// $input-height-border: $input-btn-border-width * 2 !default;
$input-height-border: $input-border-width * 2 !default;
```

* Use `$component-active-bg`, `$component-active-color` in custom-control-indicators and pagination for checked, indeterminate, and active states

* Button and Forms focus colors should be based on `$component-active-bg`

* Deprecate hover media query shim and mixins

Fixes #25195.

This never was completed or fully implemented, and the docs are inaccurate as to what browsers are currently affected by this stickied hover problem. This PR aims to update the docs and deprecate the shim from our mixins and only return the pseudo-classes. To reflect the order of these states used elsewhere (e.g., our button styles), I've also updated the order of each within the mixin.

* Mention in docs and variables that it's deprecated