Fixes #26205

Testing done

• Built Jenkins locally
• Ran Jenkins using mvn -pl war jetty:run
• Reproduced the issue by rendering an administrative monitor message
• Verified that primary buttons inside administrative monitors retain correct styling
• Confirmed button text color is no longer overridden by admin monitor link styles
• CSS-only change; no Java or Jelly logic modified

Screenshots (UI changes only)

Before

Primary button text inherits alert/link color inside administrative monitor.

After

Primary button text is white as expected, with correct primary button styling.

Proposed changelog entries

• Fix primary button text color in administrative monitors.

Proposed changelog category

/label bug, web-ui

Proposed upgrade guidelines

N/A

Submitter checklist

• The issue is well-described.
• The changelog entry is appropriate and in the imperative mood.
• There is an explanation as to why this change has no automated tests (CSS-only UI fix).
• No new public APIs or Java changes were introduced.
• UI changes do not introduce CSP regressions.
• No dependency updates are included.

Desired reviewers

@jenkinsci/core-pr-reviewers