Fix scrolling the sidebar in mobile mode.
Review Request #10750 — Created Oct. 9, 2019 and submitted
On pages without full-page content mode, the page wasn't properly set up
to allow the mobile sidebar to scroll. The sidebar's height was bound to
#containerheight, which would be based on the content height.
Only in full-page content mode would the
#containerheight be bound to
This adds a couple of extra rules to activate the correct container
height when the mobile menu is open, and to always enable sidebar
scrolling in mobile mode, ensuring that the UI always behaves as
expected regardless of the modes used on the page.
Tested the mobile scrollbar behavior on mobile mode in pages with both
standard and full-page content modes.