Describe the bug
When navigating content with the keyboard with the TAB key, all elements receiving focus should indicate this eg. by showing a visible focus ring.
Since #587, the scrollable area can be focused with the keyboard, however it does not have a visible focus indicator.

To Reproduce
Steps to reproduce the behavior:

1. Go to the Demo page
2. Use the TAB key (and SHIFT+TAB) to navigate around the page
3. See that the buttons receive a dotted outline when receiving focus
4. See that whenever the scrollable container is focus, the focus indicator seemingly vanishes

Expected behavior
It should always be visible which element has focus. When the scrollable container has focus, it should have a visible indicator.

Additional context
WCAG Success Criterion 2.4.7

Your environment