Add CSS `view-transition` to Seven and Basis for smoother page-to-page transitions

[herbdool]

Description of the need

Now that view-transition is widely supported in Chrome-based and Firefox-based browsers, I think it would be nice to include a basic setting in Seven and Basis to provide smoother page-to-page transitions.

See
https://developer.mozilla.org/en-US/docs/Web/CSS/Reference/Selectors/::view-transition and https://css-tricks.com/almanac/rules/v/view-transition/

Proposed solution

@view-transition {
  navigation: auto;
}

This will provide basic transition between pages. More configuration is possible to to specify how different sections transition, but this alone does a pretty good job.

[yorkshire-pudding]

According to this page (https://developer.mozilla.org/en-US/docs/Web/API/CSSViewTransitionRule/navigation) the navigation property is not yet supported in Firefox. Including it won't do any harm, but according to this it won't (yet) have an effect.

[avpaderno]

Actually, none of the @view-transition properties are supported by Firefox, which instead supports ::view-transition.