* Fix media-breakpoint-between
When compiling .scss that uses media-breakpoint between with xs as the lower bound or xl as the upper bound, a compilation error can occur due to $min/$max being set to null, or the resulting .css can be invalid (see issue #23965).
(This is basically the same fix that was applied to media-breakpoint-only a short time ago).
* Update _breakpoints.scss
Make houndci-bot recommended changes.
* Remove comment that duplicated some code
* Use transition mixin whenever possible
* Create a new function to reduce duplication
* Use the new `breakpoint-infix` method
Changes grid and container sizes to `px`, as the
viewport pixel size does not depend on the font size.
The actual em values were inconsistent with the docs,
while the docs were not the same as the comments:
* `sm` breakpoint was 34em (544px) not 480px.
* `lg` container max-width was 60rem (960px), less gutter than `md`.
Changed to 940px, same as Bootstrap 3.
* `xl` container max-width was 72.25rem which is 1140px not 1156px.
Changed to 1140px matching the comment but not the docs.
Addresses #17070 and #17388.
