keyboard accessibility of https://reactcommunity.org/react-tabs/

currently, there are two quite fundamental keyboard access issues on the demo page at https://reactcommunity.org/react-tabs/

• the <textarea> containing the source swallows Tab presses. once focus is in the textarea, there's no way for a keyboard user to jump back out. worse, even if the related "view source" checkbox is not checked, i.e. the textarea isn't visible, it still receives keyboard focus/is still in the regular tab cycle
• when the tab/tablist receives focus, there is no visible focus indication that this is actually the case

Video showing the issue (using Chrome on Windows)

https://user-images.githubusercontent.com/895831/173188543-011a8b79-d55b-4eeb-b907-1fb9b0033cf9.mp4

0:00 - 0:25 tabbing through the page. note the focus disappears after the "View source" checkbox. ticking the checkbox with the mouse, and carrying on tabbing, shows that tab was in the textarea (and it's stuck in there)
0:25 - 0:32 focus is on the tab/tablist, can use cursor keys to change active tab. but there's no visible indication that focus is indeed on that tab/tablist

Beginne auf der Demo-Seite unter https://reactcommunity.org/react-tabs/ und reproduziere die im Issue beschriebene Tastatursequenz, einschließlich des ausgeblendeten source textarea und des Fokuszustands von tab/tablist. Als erledigt gilt die Aufgabe, wenn Tastaturbenutzer den source-Bereich normal verlassen können, ausgeblendete Inhalte nicht im tab-Zyklus enthalten sind und der Fokus auf tab oder tablist sichtbar angezeigt wird.