Clarify migration docs to remove mention of .table-responsive being for the parent element vs the table element itself (#25539)

Fixes #25413

* Prevent focus into closed offcanvas

- Fixes typo with "with at" in "horizontal with at the small breakpoint"

* Move helpful code comments

* Add .carousel-fade option to Sass

* Document example of the fade carousel

* more logical warning of the .active class on carousel items

* Add .dropdown-item-text class

* Add example of plain text within a .dropdown-menu, too

* reorganize, simple/clearer headings

Currently bootstrap only provides 4 variations of `width` and `height` css utilities, which are:

1. 25%
2. 50%
3. 75%
4. 100%.

Here, I'm adding `auto` to the list. This is useful when we need to reset the width/height value
back to the browser default value at some point.

Closes #25313

Less on 2 symbols

Merge branch 'borderless-table' of https://github.com/Varunram/bootstrap into Varunram-borderless-table

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

Removed '**Animated progress bars don't work in Opera 12**—as they don't support CSS3 animations.' note.

Bootstrap 4 doesn't (and doesn't need to) support the ancient Opera 12 released in 2012 with a 0.04% marketshare so no need to mention.

Convert them to 8-bit and compress them with optipng and zopflipng.

Before: 902 KB (923,969 bytes)
After:  431 KB (441,372 bytes)