* Prevent print utils from overriding all other display utils
Fixes#25221.
I agree with the referenced issue—this is unexpected and also causes a serious bug when mixed with other utility classes. This wasn't an issue in v3 given we had different utilities for hiding that weren't focused on display property.
* Add printing changes to migration docs
* unrelated heading sentence case change
* List out all .d-print- classes
* Update the form focus mixin to use a manual `$enable-shadows` check so we can always ensure a focus state for accessibility and consistency
* - Add new `$input-btn-focus-width` and `$input-btn-focus-color` variables.
- Replace separate `$btn-focus-box-shadow` and `$input-focus-box-shadow`
variables with unified `$input-btn-focus-box-shadow` to match our
combined variables approach elsewhere.
* Put new focus width var to use in buttons mixins
* use new button input-box shadow var
* Add a new mixin for quickly adding linear gradient to components when $enable-gradients is set to true
* use correct var
* fix focus shadows in button mixins
* Add opt-in gradients to alerts, buttons, carousel, custom radios and checkboxes, custom file input, and dropdown items
* Generate .bg-gradient- utilities
* add headings to colors page and document bg-gradient utils
* update the button color for active status, check with yiq as it's done for basic state and hover state
The class ".border" (css/utilities/_borders.scss) is set the border-color to "$gray-200".
So I see that it would be nice to create a variable for the border color "$border-color". Because the default border should not always be "gray-200".
Another thing, there is a "$border-width" variable. Would not it be better to use this variable to set the default width of the border?
— Moves print display utils to display utils file
— Removes all other .hidden- utils
— Expands on .invisible and it's mixin to provide options for visibility: visible and visibility: hidden
- Renames .pos-f-t to .fixed-top, adds .fixed-bottom and .sticky-top
- Updates utilities Sass to be split across more files (one for position, sizing, and spacing)
- Adds new flexbox.md file to utilities docs
- Adds a `breakpoints.yml` data file for easier output of responsive classes in the docs. Will put this to use on other pages soon.
- Adds hella flex utils. There are some dupes for now, but they'll get removed in time.
