* 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

[Docs] Clarify suggested use of custom validation styles, add note about resetting form appearance after validation (#25628)

* Expand/clarify recommendation for using custom validation styles

Seems support for correctly announcing browser default navigation bubbles/notifications has improved recently. Now it seems only Chrome (at least on Win and Android, not tested on macOS) is the odd one out.

However, we should really make sure the custom validation messages are also tied correctly to their relevant form controls - need to dig out the PR that will ensure that.

* Add note about resetting form appearance after submission

xref https://github.com/twbs/bootstrap/issues/25626

Opera 19 was released in January 2014 and auto-updates so I suggest no need to mention about browser support for this old version.

* Add additional form validation examples

Fixes #24811.

This adds .valid-feedback to our custom styles and server side examples; previously we ommitted this to suggest you don't always need valid feedback. In addition, this adds examples of the .{valid|invalid}-tooltip classes with a new subsection in the Validation docs.

* Update validation tooltip styles to remove fixed width; instead should retain itself to the parent element

* update ids

* finish docs paragraph, mention position: relative

"Choose file ..." text is now written inside the label tag, so the translation is outside the css scope. 
$custom-file-text variable should only contain "Browse" translations.

- Changes the wrapping label to a div so we can style the label instead of another element while also supporting form validation.
- Fixes form validation styles for custom file input (closes #24831).
- Updates docs with validation styles (also adding example feedback text while I was there) and new how it works section.

Adds some additional context on `.form-group` usage

* match layout behaviors

* ditch the indicator as separate element for psuedo-elements on the label

* move disabled to attribute only on input

* redo default inline check to support new markup

* redo inline forms

* clean up vars

* update validation mixin to new structure

* update checks in docs

* linting for for/id attributes

* Rewrite input group component

* Set the feedback to 100% width for input group

* Move from .row to .form-row for tighter layout

* no need for custom feedback here, we're using browser messaging

* add input group to validation examples

* add note about validating multiple

* migration note added

* chore: sync with twbs (#1)

* Make styling of grouped option buttons class-based

Referencing #23728, styling grouped radio and checkbox buttons should not require the data-toggle attribute.

* Fix installing deps in our webpack docs

* Fix nested cards on card group (#24766)

* Update popper.js to v1.12.9. (#24797)

* Don't run postcss for `dist/css/*.min.css` files. (#24676)

* Change the text color to dark on bg color warning examples (#24805)

* Remove unused file and bundle ie-emulation-modes-warning.js with docs.min.js (#24825)

* Remove the unused assets/js/ie10-viewport-bug-workaround.js.

* Combine ie-emulation-modes-warning.js with docs.min.js.

* Typos in grid.md (#24828)

Fixed typos in offsetting section of grid.md

* Fix dropup example code

* Update devDependencies. (#24829)

* Add support for fractional viewport widths (zoom/high-dpi displays) (#24299)

* Change breakpoint  max- calculation to fr...

We could tell folks to nix the class, we could tell them to override it, or we could add another modifier of some kind to address this. None of them seem particularly useful, but the padding override feels the most approachable and clearly documentable. Added this here to close #24844.

* Add support for size attribute on custom selects

* Add large custom select, document it and the small variant

* fix custom select focus state

* fix custom file input focus styles

* remove empty line

Fixes #24739

* fixes migration forms guides

* removes container from Horizontal form

* adds col-form-label sizes on form docs

* removes .form-control-label from forms.scss

* add note to migration

* use a trailing slash when possible
* use https when possible
* remove a few redirected links
* consistently use `https://popper.js.org/`
* fix `iconUrl` in nuget files
* change Jekyll Windows guide to the official one

See http://caniuse.com/#feat=pointer-events

Fixes https://github.com/twbs/bootstrap/issues/23773