Revert "fixes #17379: override search input box-sizing to match our global overrides"

This reverts commits 468a9d93 & 57998dc2.

https://github.com/necolas/normalize.css/pull/496 has made this override unnecessary.

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Bump Normalize to https://github.com/necolas/normalize.css/commit/fe567632afcf8afcf17925ab2a507ed87504cce8

So as to pull in https://github.com/necolas/normalize.css/pull/496

Closes #18887

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gradient-{horizontal=>x}[-three-colors]
gradient-{vertical=>y}[-three-colors]

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See issue: https://github.com/twbs/bootstrap/issues/18385

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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Erratum of #18778

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Fixes #18609

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In IE9-11, prevent breadcrumb separator from getting underlined on :hover when not using <ol> markup

Fixes #18733 in IE9-11
Also adds comments to the code explaining this and #18740.

In modern browsers, prevent breadcrumb separator from getting underlined on :hover when not using <ol> markup

Fixes #18733, except in IE9-11
Closes #18740

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