Small screen TOC is not keyboard navigable

[stevejpurves]

Describe the bug

context
On a smaller screen, when I attempt to access the table of contents using the keyboard

expectation
I expected to be able to open the TOC with the first item focussed and use the keyboard ot navigate the items.

bug
But instead the contents of the TOC does not get focus and nor does it respond to keyboard events, in fact the main article still has keyboard focus.

problem
This is an accessbility problem for keyboard users.

Reproduce the bug

List your environment

No response

[rowanc1]

This has been fixed in #254.