Smooth scrolling containers

Example of a table of contents navigation with a container using smooth-scrolling.

Setup:

1. 'scroll-behavior: smooth' is being used to smoothly scroll main contents.
2. element.scrollIntoView() is being used to make main content visible.
3. element.scrollIntoView() is being used make table of contents item visible.

Issue: When element.scrollIntoView is called from within two different scrolling containers then the second scrollIntoView call will interrupt the first, if the first is using smooth-scrolling.

Repro:

1. Click the 'smooth' links below to smoothly scroll the main content into view.
2. Observe that it does not scroll.
3. Observe that 'instant' scrolling does work.