In about 'Reboot', it says "moving **from** `rem` **to** `em` units. It should be moving from `em` to `rem`.

Changed `box-sizing: border` to `box-sizing: border-box`

Fixes #18813
Closes #20187

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The `remote` option and the accompanying event have been removed.

Update tags/labels/badges migration docs to mention class and change in behavior for alignment in list groups

Fixes #18705: Clarify removal of .help-text and update changes to .form-group for horizontal layouts

Signed-off-by: Chris Lamb <chris@chris-lamb.co.uk>

Closes #19561
Closes #19567
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Refs #19080

Refs #18767
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Use new `.breadcrumb-item` class instead of child selectors and `li` tag selectors,
so as to no longer require the usage of `<ol>`-based markup.

Rename variables to follow naming conventions:
* $breadcrumb-padding-vertical => $breadcrumb-padding-y
* $breadcrumb-padding-horizontal => $breadcrumb-padding-x

Introduce new variable: $breadcrumb-item-padding

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Fixes #18505
Closes #18509

Refs #18110

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