Align DataTables header hover styling with Jenkins core

[Haschwalt29]

Description

This pull request aligns the DataTables column header hover styling with the
hover behavior used in Jenkins core tables.

The change removes the custom outline-based hover effect and replaces it with
a Jenkins style hover treatment based on background highlighting and a subtle
inset border, using existing Jenkins CSS variables. This improves visual
consistency between DataTables based tables and Jenkins dashboard tables while
keeping the styling minimal and theme aware.

Fixes #664

Testing done

This change was tested manually, as it is a frontend CSS only change.

• Verified the DataTables column header hover behavior using a local HTML test
  page that loads the updated jenkins-style.css.
• Compared the hover behavior against Jenkins dashboard table column headers
  as a visual reference.
• Verified that the hover styling adapts correctly in both light and dark
  themes using prefers-color-scheme emulation.
• Confirmed that no hard-coded colors are used and that the styling relies
  solely on Jenkins CSS variables.

Screenshots demonstrating the hover behavior in light and dark themes are
attached below.

• Jenkins dashboard column header hover (reference)

• DataTables column header hover after this change

Submitter checklist

• Make sure you are opening from a topic/feature/bugfix 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 (not applicable)
• Ensure you have provided tests that demonstrate the feature works or the issue is fixed
  (manual testing performed; automated tests are not applicable for this CSS-only change)

[uhafner]

It does not seem to have an effect on a real world example:

[Haschwalt29]

@uhafner Thanks for checking
I am positive I made the necessary changes, Could you please share which page or DataTables instance you tested this on?

[uhafner]

I tried this https://ci.jenkins.io/job/Plugins/job/analysis-model/job/main/687/coverage/ and this https://ci.jenkins.io/job/Plugins/job/analysis-model/job/main/687/java/

[uhafner]

This does not work either. You can test locally by using https://github.com/uhafner/warnings-ng-plugin-devenv or create a project that records code coverage results.

[uhafner]

Any plans to finish this PR?

[Haschwalt29]

Any plans to finish this PR?

I haven’t been able to successfully set up and test Jenkins locally in a way that lets me reproduce and verify the DataTables hover behavior (particularly for the coverage-related pages). Without a working local Jenkins setup, I’m not confident that I can properly validate or finish this change.

Because of that, I don’t think I’ll be able to complete this PR in the near term. I’m happy to close it for now to avoid blocking things, and revisit it once I’m able to set up proper local testing.

Please let me know how you’d prefer to proceed.

[uhafner]

Oo, no worries. I set the PR to draft, maybe I find some time after FOSDEM to finish the changes...