Fix unknown style

[eromano]

Please check if the PR fulfills these requirements

• The commit message follows our guidelines
• Tests for the changes have been added (for bug fixes / features)
• Docs have been added / updated (for bug fixes / features)

What kind of change does this PR introduce? (check one with "x")

• Bugfix
• Feature
• Code style update (formatting, local variables)
• Refactoring (no functional changes, no api changes)
• Build related changes
• Documentation
• Other... Please describe:

What is the current behaviour? (You can also link to an open issue here)
For dark theming the unknown text field is not readable

What is the new behaviour?

Does this PR introduce a breaking change? (check one with "x")

• Yes
• No

If this PR contains a breaking change, please describe the impact and migration path for existing applications: ...

Other information:

[codecov-commenter]

Codecov Report

Merging #5810 into develop will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff            @@
##           develop    #5810   +/-   ##
========================================
  Coverage    83.91%   83.91%           
========================================
  Files          963      963           
  Lines        27237    27237           
  Branches      3799     3799           
========================================
  Hits         22857    22857           
  Misses        3244     3244           
  Partials      1136     1136           

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