Remove stray spaces from modal/using-grid-system sample code

Input group sizes: Properly position `.form-control-feedback`

Fixes #15074

Update .visible* classes to use !important on table elements

Conflicts:
	dist/css/bootstrap.css.map
	dist/css/bootstrap.min.css

Darker style focus/hover on active buttons

There is no jshint:src task

Remove wrong role="tabpanel" from docs

As per discussion on https://github.com/w3c/wai-wcag-quickref/issues/2
and #13554

Make .bg-variant adjust :focus color in addition to :hover color

JSCS: Add "disallowSpacesInFunctionDeclaration"

Valid:

    function a() {}

Invalid:

    function a () {}

Jumbotron: Putting heading font size in variables to allow for easier overrides

Closes #16047 by merging a tweaked version of it.

Only disable pointer-events on disabled <a> btns

remove redundant aria-hidden usage from Modals

Document how to disable transitions in jQuery plugins

Properly document $(...).tab('show') method

[skip sauce]

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Currently, hovering with mouse or setting focus on a button which is
active has same styling as on a non-active button. This results in
problems for keyboard users, who set focus on a toggle and activate it,
but cannot visually see that their action had any effect. Ditto for
mouse users hovering over a toggle and clicking it. This adds an
explicit additional style for focus/hover on active buttons.
Note that this does not address issues of browser focus remaining on a
button after a mouse click (e.g. #13971), as this will likely require
extra JavaScript to fix.