TAB key navigation has extra tabstop with no focus indicator

[mbgower]

In both FF and Chrome, when I tab from a header on an expanded panel, the focus leaves the header but does not appear to go anywhere. Especially for 'rookie' users, this is highly confusing at some point. The user must press TAB again to put focus on the first focusable element.
This 'missing' focus item occurs using SHIFT+TAB as well.

[ryuran]

Good point, when panel is open.
If you press tab, focus move to hidden title.
So it's not visible for user.

@nico3333fr do you have an idea to manage this focus?

You can maybe show it by css on focus. But it will causing reflow.
Or hide it by an other way to keep focus ring visible.