Co-authored-by: XhmikosR <xhmikosr@gmail.com>

- Remove redundant `display: inline-block` from flex children
- Remove `line-height: inherit;` which is the default value of `line-height`
- Use flex shorthand
- Improve background shorthand
- Fix removed brand margin caused by requiring containers in navbars

- Enable RFS
- Add documentation
- Disable doc font size overrides

* 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