Allow optional breakpoint arguments to be passed on to nested media query mixins

Use proper units when adding/subtracting lengths

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Rename padding local vars per new naming convention
/fyi @mdo

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Add Wall of Browser Bugs entry for #18859

See https://bugs.webkit.org/show_bug.cgi?id=153056
Refs #18859
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Modal: Respect $enable-rounded setting
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See issue: https://github.com/twbs/bootstrap/issues/18385

Refs #18782
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remove link to the pager component

Refer to open successor Chrome bug in Accessibility docs

see https://github.com/twbs/bootstrap/pull/18782

https://crbug.com/262171 was closed as a duplicate of https://crbug.com/454172

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Add SRI hashes for jQuery and Tether in docs

Workaround for https://github.com/jzaefferer/grunt-html/issues/86

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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

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Remove About > Accessibility, add to Get Started

Docs: Add missing pages to "Getting started" TOC

Fixes #17986
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Extract $btn-active-box-shadow variable & refactor accordingly

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

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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

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v4: Add Liberation Mono to the code font stack

Fixes #18609

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Fixed by way of https://webkit.org/b/152803
Thanks Google Translate (I guess) and WebKit Team!
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Refs #16814
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