Remove old CSS variable fallbacks

[janfaracik]

Small one to remove old CSS variable fallbacks now that our baseline is high enough. Also standardised some of the variables so that the search bar and cards look consistent.

Testing done

• Works as expected

Submitter checklist

• Make sure you are opening from a topic/feature/bugfix branch (right side) and not your main branch!
• Ensure that the pull request title represents the desired changelog entry
• Please describe what you did
• Link to relevant issues in GitHub or Jira
• Link to relevant pull requests, esp. upstream and downstream changes
• Ensure you have provided tests that demonstrate the feature works or the issue is fixed

[lewisbirks]

Sounds good to me, the pom defines the current version as 2.528