Accessibility section formatting

[mikeapp]

For https://preview.iiif.io/api/prezi-4/presentation/4.0/#accessibility

• The "Key points" section has a green background
• On mouseover of the Accessibility header, I don't see the anchor icon appear that allows me to copy the link to the section. This is normal for top-level headers, but since we don't have a second-level header for this section I can only copy the link from the browser nav bar.

(Mac Safari)

[mikeapp]

Green background also after the example in https://preview.iiif.io/api/prezi-4/presentation/4.0/#3d-comments-with-cameras