[ci skip]

Switch to actually-Safari-specific CSS hack for iOS temporal input fix

Switch to actually-Safari-specific CSS hack when fixing vertical alignment of temporal input text in iOS Safari

See http://browserbu.gs/css-hacks/webkit-full-page-media/
Fixes #17308

[skip sauce]
[skip validator]

Remove About > Accessibility, add to Get Started

Docs: Add missing pages to "Getting started" TOC

Fixes #17986
[skip sauce]

Extract $btn-active-box-shadow variable & refactor accordingly

[skip sauce]
[skip validator]

Add $progress-box-shadow variable
/fyi @mdo

[skip sauce]
[skip validator]

Introduce $tooltip-padding & $tooltip-padding-x vars

Currently, there is no actual accessibility page, so this avoids a 404
in the docs. More fundamentally, though, it makes more sense for
accessibility advice to be directly integrated in the docs (which we're
doing, for the most part - though we should ensure that we do
cover/mention everything where appropriate), so there's no need for a
separate accessibility page.

Erratum of #18778

[skip sauce]
[skip validator]

v4: Add Liberation Mono to the code font stack

Fixes #18609

[skip sauce]
[skip validator]

Fixed by way of https://webkit.org/b/152803
Thanks Google Translate (I guess) and WebKit Team!
[ci skip]

Refs #16814
[ci skip]

Add variables for spacing of .btn-toolbar and split-button dropdown toggles

Flexbox grid column wrapping bug

Add nested definition list to docs example

Add comprehensive `.form-control` example(/testcase) to docs

Refs #18458
[skip sauce]

[skip sauce]

[skip sauce]