- Remove `.sr-only` span for previous/next page, there is already`aria-label`
- Add `aria-disabled="true"` and `aria-current="page"`

This allows the user to make a container (ideally) to use viewport height and width and allow better vertical/horizontal alignments of elements.

Fixes #25870

This change follows exactly what was done for the `$grays`, `$colors`, and `$theme-colors` lists in #23260. This allows for easy addition of new breakpoints or grid containers also.

Leftover from after 43c20b91.

Now that we don't have the ToC issue with the examples' headers in ToC, we can safely do this.no_toc_section_class

If I want to customise the breakpoints using `em`, I get compatibility errors.

It is good practice to set breakpoints in `em` instead of `px` when users use browser scaling.
See https://zellwk.com/blog/media-query-units/#concluding-the-experiments for more information why someone would like to do this. Only Safari users can get annoyed: https://adamwathan.me/dont-use-em-for-media-queries/

In any case, using a unitless number at line 42 would be very convenient.

The current documentation for .flex-fill indicated that the flex
items would have equal widths, regardless of content. This update
ensures that the documentation reflects the fact that the width
of the flex items depends on their actual content.

This reverts commit 1c78f703.

Unfortunately some Linux distros use an ancient git version and this change requires git >= 2.10.

Define new variable for card header color

Removes the grid.css file of the grid example and makes use of utility classes

The outline button variant mixin should use the hover mixin, as does the non-outline version.

user-select has no effect on before/after pseudo elements

When gradients are enabled there is still a hover state on disabled
buttons since the hover rules apply to background-image and disabled
rules apply to background-color. This applies the logic already present
in dropdowns to buttons. This fix was originally proposed by @ysds.

Requires jekyll-toc v0.8.0.

* remove unused rules
* use Sass nesting in more places
* use the core mixins in more places
* use the color variables more