Demo unexpectedly traps focus

One can navigate into "Dog, Cat, Turtle" button group with Tab, but Shift+Tab only cycles buttons inside the section.

Reproduction:
1. Navigate to https://ai.github.io/keyux/
2. Click Cat button
3. Press Shift+Tab several times

Expected:
One should be able to navigate to Android button

Actual:
Shift+Tab only cycles Dog and Cat buttons