The page has a shadow root that in turn contains two shadow roots. So we can
check behaviour with both nested roots and younger/older sibling roots. The
various sections are highlighted with colored borders to make it more obvious
where each element comes from. Default to pushing the content off the first
screen, to test that scrolling to the elements works.
stuff
Parent
Contents
Older Child
As the older child of a nested shadow root, this is the most likely
to go wrong bit of the page, so we'll concentrate our tests here.