Add callouts about using light colors ideally on a dark background

Fix redirects

* Split up dropdown sizing docs to improve rendering

- Drop the included .btn-toolbar, no need
- Split large and small button examples

* Replace visually hidden span with aria-current in tests

* Remove redundant visually hidden "(current)" when `aria-current` already used

Closes #31891

* feature(spinners): slow down spinners when prefers-reduced-motion

* docs(spinners): add reduced motion callout and mention slowing down in accessibility page

* Update spinners.md

* docs(accessibility): rewording

Co-authored-by: XhmikosR <xhmikosr@gmail.com>
Co-authored-by: Patrick H. Lauke <redux@splintered.co.uk>

* docs(forms): use a legend for fieldset instead of aria-label

* docs(forms): fix incorrect legend nesting in fieldset

carousel: add missing `to` and `nextwhenvisible` description 

Closes #22610

* Expand advice for anchor-based controls

* Expand accessibility note in input group

* Correct statement about validation, fix server example

* Tweak label > accessible name

Co-authored-by: XhmikosR <xhmikosr@gmail.com>
Co-authored-by: Mark Otto <markd.otto@gmail.com>

Remove the class `.nav-item` from `.nav-link` inside the non `ul` or `ol` based navs.
This makes the consistency for `.nav-item` (This class will not be required on the `.nav-link`).
`.nav-item` was only required when you use `.nav-fill` or `.nav-justified` on the `.nav`. In other cases, it was redundant. And the purpose of `.nav-item` on `.nav-link`s can be achieved via flexbox utilities as well (Mentioned in the docs also).

Add role="dialog" in modals via JavaScript