High contrast mode findings

[fscholdei]

Proposed changes

Correct high contrast mode findings scm-manager/scm-manager#1892.

Your checklist for this pull request

Contributor:

• PR is well described and the description can be used as a commit message on squash
• Related issues linked to PR if existing and labels set
• New code is covered with unit tests
• New ui components are tested inside the storybook (module ui-components only)
• Changelog entry file created in gradle/changelog or CHANGELOG.md is updated for plugins
• Feature has been tested with different permissions
• Documentation updated (only necessary for new features or changed behaviour)

Reviewer:

• The clean code principles are respected (CleanCode)
• All new code/logic is implemented on the right spot / "Should this be done here?"
• UI changes fits into the layout
• The UI views / components are responsive (mobile views)
• Correct translations are available

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• Branch is green/blue on Jenkins
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