See https://bugs.webkit.org/show_bug.cgi?id=158342
Fixes #17695

With apologies, copy/paste error following on from trying to fix conflicting Hound/Travis checks for https://github.com/twbs/bootstrap/pull/20821/ slipped through before I noticed them.

Update print styles borrowed from h5bp

Change `hidden-sm-up` to `hidden-md-up` as the clearfix divs should be visible on both `xs` and `sm` devices (widths of 6 columns).

* Fixes #20775 without adding extra width and an important flag

* Since we're now getting the extend, we don't need the extra position relative

* rerrange

* getting min-height from the extend already

Merge branch 'customizable-grid-gutters-per-breakpoint' of https://github.com/pixelbandito/bootstrap into pixelbandito-customizable-grid-gutters-per-breakpoint

Only override input border-radius as part of .form-control to avoid bug with iOS Safari (alt fix for #20247) (#20695)

Fixes #20118: Add and use Sass variables to control the color of our embedded SVGs for custom form elements (#20700)

* Fixes #19784: Move from pixels to rems, add a margin-bottom: 0; to keep things aligned

* lintiong

- Fixes #20298 for vertical button group spacing
- Fixes #20784 for horizontal (default) button group spacing
- Alternate fix to #20823 which only applied a fix for vertical button groups

* descriptions for getting started pages

* descriptions for layout

* add content page descriptions

* more descriptions, updates to some existing ones

* correct site url

* add social stuff to config for twitter cards

* add twitter meta tags; use large image for homepage and regular card for all others

* add the assets

* more site config

* more social shiz to partial, remove existing meta for the partial, remove page title from homepage for simpler if statements

most notable change:
- fixes print/print preview crash in IE11 (caused by `*:first-line`
selector)

Add Edge#9011176 bug (visual artifacts in scrollable dialogs)

https://developer.microsoft.com/en-us/microsoft-edge/platform/issues/8282613/ has been marked as Fixed.
Refs #20335.

[skip sauce]

* Have same margin for <hN> as a <div> on .card-headers
Related #18726

When you use a `<hN>` as `.card-header` there is `margin-bottom: .5rem` added. The changes set the margin-bottom to 0
* Removed space