Having variables initialised from start `_isTransitioning` is better.
Would be better to add an eslint rule to check for undeclared variables use.
Reordered enter checks for `show` and `hide` by priority.

Only run `coveralls` and `check-broken-links` tasks when we run the Test phase.

I'm using Tab.js with remove function and get an error "TypeError: container is undefined [more info]", with this check the error is fixed.

- 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.