Feature/oxui 288 as a user i have a number sign section as fallback in the thumb index

Feature checklist

• created mock-ups first
• written tests
• written some documentation (if needed)
• added some metrics events (if useful)
• checked on mobile devices (at least in dev tools)
• tested accessibility (semantically correct markup, source-/tab-order)?
• flown over the uxchecklist
• passed usability test (friendly user test)

Implementation notes

• after-merge: needs software change request