fix(pagination):improve focus style to meet WCAG 2.2 AA

[dancormier]

Addresses STACKS-544

Technical notes

You'll notice that this PR achieves the focus style mainly with box-shadow:

   box-shadow: inset 0 0 0 var(--su-static2) var(--theme-secondary-400), inset 0 0 0 var(--su-static4) var(--black-050);
    …
   outline: var(--su-static2) solid transparent;

This is because box-shadow tends to align more consistently. Additionally, a transparent outline is used to ensure that an outline doesn't render when expected but can still be rendered in forced-color modes (see https://blogs.windows.com/msedgedev/2020/09/17/styling-for-windows-high-contrast-with-new-standards-for-forced-colors/#gist105426765).

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[dancormier]

Visually, everything looks good, from other examples I'm seeing online I think we need Focus to land on the selected/active page number as well. In the preview, it skips over page 1 when I tab through the elements.

The current page is indicated by aria-current="page".

Other resource

Unless I'm missing something...

I've added the focus style on the pagination item with .is-selected, but it would only be focused if it were rendered as a link. We've historically omitted the link on the active element, though I can change that (it would only change that in the docs and consumers of the component would need to update if that want to match that). I'll update the docs to include a linked selected pagination item.

[dancormier]

@CGuindon I've update the pagination docs to include a linked selected pagination item and I've added the visually hidden "page" text inspired by the W3C design system:

For all pagination links excluding the current page, page is added to provide additional context to the link wording for users of Assistive Technology.

[CGuindon]

@dancormier Would it be possible to add a test for this? So that any pagination buttons that are missing this piece in core would then show up in our automated tests list of issues with exact locations? (or am I dreaming to big)

[dancormier]

@dancormier Would it be possible to add a test for this? So that any pagination buttons that are missing this piece in core would then show up in our automated tests list of issues with exact locations? (or am I dreaming to big)

Dreaming big is good! That said, I think automated accessibility testing may catch failures like aria-current="page" missing, but I'm not 100% sure about that. As far as using an anchor for the current page, I don't believe that's an explicit requirement for WCAG AA (just a decent practice) so automated tests for sure wouldn't call that out.

It's pretty hard to enforce our components to be marked up exactly as we'd want in our consumer code unless they're using something like a razor or svelte component that handles the markup for the consumer. At some point, we'll probably want to work with Core to help design their accessibility tests broadly which may help with this, but I think this will probably need to be manual for the moment.