* Explore responsive display utils, but with a twist: lowest breakpoint has no breakpoint modifier in the class name
* make floats use the same format, add float-none mixin

* descriptions for getting started pages

* descriptions for layout

* add content page descriptions

* more descriptions, updates to some existing ones

* correct site url

* add social stuff to config for twitter cards

* add twitter meta tags; use large image for homepage and regular card for all others

* add the assets

* more site config

* more social shiz to partial, remove existing meta for the partial, remove page title from homepage for simpler if statements

- Move and rename .img-rounded to .rounded, .img-circle to .rounded-circle
- Add new .rounded-{direction} utils
- New docs pages for border utils with TBD comments for the border property
- Removes most image examples for rounding from the content/images docs in favor of new docs page

* Fix docs for heading sizes (sizes here were from v3)
* Added rem sizes to header size docs
* Fixed erroneous px sizes

- Add inverse examples for all variants
- Use rgba() colors for hover and accent states for easy usage in inverse styles

- Change some things around, add some copy
- Include table variant styles for the inverse tables thanks to bg and color utils

[skip sauce]

Closes #19339
Refs #19102, #19443, #19665
[skip sauce]

Replace the leftover instances with .m-x-auto (and .d-block when necessary)
Closes #19665
Refs #19102
[skip sauce]

- Add/replace callout for color and AT with include

[skip sauce]

Fixup for 27ba4beb
/fyi @mdo
[skip sauce]

- Using the grid classes, they still need clearfixes since rows aren't injected between them all
- Update docs to fix broken classes

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These are available in _type.scss but not documented.  These classes are useful for styling without adding semantics.

Refs #18458
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It has been removed from the HTML specification: https://github.com/whatwg/html/issues/336
Only Presto Opera ever implemented a special UI for it.

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also, stray "blocks" in the "Sample output", which doesn't seem to
belong there.

use `<code>` (as it's still semantically code that we're marking up) and
make the example actually multiple lines...

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