Custom v4 CSS builds

- Credit: @adammacias
- Originally proposed in #16499 with previous commit

- Credit: @adammacias
- Fixes #16499

Fix hover border covering active in pagination

Fix #16646

- drop the index pages save for examples
- comment out the extend section for now
- fix up spacing fix on team list

Add role="document" to modal dialog content

to include a note about `role="document"`

Initial fix to generalise use of modals. Generally, true role="dialog"
containers would require only forms/controls as content, with all other
text correctly and explicitly associated via
aria-labelledby/aria-describedby and similar...but as authors use modals
also as generic overlays, this extra role is required to get AT
(particularly NVDA) out of "forms" mode and reenable reading keys

Fix asymmetry between dropup and dropdown carets.