...as it always evaluates to true

The default font weight value for <strong> <br> in reboot was
set by a fixed value we now use the variable $font-weight-bolder
to let users override this value.

Dynamically set/remove `aria-modal="true"` when a modal is shown/hidden

This reverts commit 11da1601.

This is no longer needed with jekyll-toc 0.9.1.

We have /site/.eslintrc.json that covers this.

This reverts commit b442ce31.

Callouts are already excluded from ToC, but due to a limitation in jekyll-toc they are still being included.

We should revisit this if the bug is fixed later.

It's pretty small compressed; a little less than 1 KB with gzip.

Image by @mdo.

This should reduce the amount of bytes for non-2x displays.

It's been macOS for 3 years now and we use just 'macOS' elsewhere in the Bootstrap documentation.
https://en.wikipedia.org/wiki/MacOS

* prevent text selection for floating labels
  * expand the click target by no selecting the label text
* use `pointer-events: none;` instead of `user-select`
  * thx @MartijnCuppens

This reverts commit b04f97f6.