[a11y] 11.2.4.7 Focus visible

[tschiebel]

audit: https://infinite.owncloud.com/s/qSvYucPltEYUhhc

https://github.com/BIK-BITV/BIK-App-Test/tree/main/Pr%C3%BCfschritte/de
https://www.etsi.org/deliver/etsi_en/301500_301599/301549/03.02.01_60/en_301549v030201p.pdf

Note: If the focus highlighting is done exclusively by a color change,
the contrast between the focused and unfocused state should be sufficient.
It is recommended that the contrast ratio is at least 3:1.

Personal Space

• For all buttons where the keyboard focus has been implemented by changing the background
  background color, the keyboard focus is difficult to see. The
  contrast between the focused and unfocused state is significantly below the recommended
  the recommended contrast ratio of 3:1.
  

Menu, Shared with me, Shared with others

• See commentary on Personal Space.

Spaces

• The space buttons have a barely visible keyboard focus.