- Simpler main nav on all pages
- Back to purple masthead on homepage instead of dark graphite
- Active link styles on the main nav
- Cleaned up sidebar nav
- New docs layout name
- Homepage copy edits
- Updated bright purple docs color

fixes #16902: remove the .container-fluid from the grid system in modal example since it's doubling up padding

Shouldn't really happen, but China for example has blocked Google so this should help.

Also, include visible <label> as a suggestion in the accessibility
callout.

They're no longer on Folsom St.

[skip sauce]

[skip sauce]

[skip sauce]

X-Ref #13969

Fix #16632

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

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