- Use a semitransparent gradient from light to dark which works on any background-color
- Store the gradient as a custom property (--bs-gradient)
- Remove `.bg-gradient-*` variants in favour of `.bg-gradient` which works even when `$enable-gradients` are enabled
- Add gradients to navbar, active page links and badges when gradients are enabled

Replaces a custom hsla() value (dunno what I was thinking when I added this) with a reassigned existing variable. This variable goes up the stack and attaches to the component-active-bg variable, derived from our primary color out of the box. Fixes #30646.

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

- Rename `$enable-prefers-reduced-motion-media-query` to `$enable-reduced-motion`
- Rename `$enable-pointer-cursor-for-buttons` to `$enable-button-pointers`

Co-authored-by: Martijn Cuppens <martijn.cuppens@gmail.com>

* Disable negative margins by default

* Use shorter enable variable

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

Co-authored-by: Martijn Cuppens <martijn.cuppens@gmail.com>

- Define background properties in `.form-check-input`
- Use `background-size: contain` to simplify background sizes (especially for those with linear gradients)
- Remove double `color-adjust`
- Adjust svgs to 20x20 box. This way the strokes aren't rescaled.

- Convert to Sass map
- Consolidate font-weights into single option (matching line-height for them)
- Add two new sizes and create a new scale
- Update migration docs

Co-authored-by: Martijn Cuppens <martijn.cuppens@gmail.com>

- Updates mentions of number and exact tiers
- Updates grid example to include xxl container
- Adds some scss-docs references
- Cleans up other grid mentions and docs
- Updates navbar example to include an expand at XXL variant

- Staring at my laptop, I realized I'm wasting away space. This adds a 
significant amount of CSS, but it feels right already.
- Added the xxl tier with a width that divides by 12
- Motivation was originally trying to have a third column for our toc so 
that our docs are more useful

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

Co-authored-by: Martijn Cuppens <martijn.cuppens@gmail.com>

Co-authored-by: David Van Doninck <david.vandoninck@intracto.com>
Co-authored-by: XhmikosR <xhmikosr@gmail.com>
Co-authored-by: Martijn Cuppens <martijn.cuppens@gmail.com>

Co-authored-by: Martijn Cuppens <martijn.cuppens@gmail.com>

Fixes beeing able to control `.is-valid` & `.is-invalid` input:focus opacity

This reverts commit cd7e5d11

.

Co-authored-by: Martijn Cuppens <martijn.cuppens@gmail.com>