Fix anchor links being obscured by header

[Gautam-aman]

Fixes #16803

Testing done

-Started Jenkins locally from the built WAR
-Navigated to configuration pages using anchor URLs
-Verified that anchored sections are fully visible and not obscured by the fixed header

Screenshots (UI changes only)

Proposed changelog entries

N/A – UI-only CSS fix with no user-facing functional change.

Proposed changelog category

(skip)

Proposed upgrade guidelines

N/A – no upgrade or migration impact.

Submitter checklist

• The issue, if it exists, is well-described.
• The changelog entries and upgrade guidelines are appropriate for the affected audience.
• There is automated testing or an explanation as to why this change has no tests.
  This is a CSS-only layout fix; Jenkins does not have automated coverage for anchor scroll positioning.
• New public classes, fields, and methods are annotated with @Restricted or have @since TODO Javadocs, as appropriate.
• New deprecations are annotated with @Deprecated(since = "TODO") or @Deprecated(forRemoval = true, since = "TODO"), if applicable.
• UI changes do not introduce regressions when enforcing the current default rules of Content Security Policy Plugin. In particular, new or substantially changed JavaScript is not defined inline and does not call eval to ease future introduction of Content Security Policy (CSP) directives (see documentation).
• For dependency updates, there are links to external changelogs and, if possible, full differentials.
• For new APIs and extension points, there is a link to at least one consumer.

Desired reviewers

@mention

Before the changes are marked as ready-for-merge:

Maintainer checklist

• There are at least two (2) approvals for the pull request and no outstanding requests for change.
• Conversations in the pull request are over, or it is explicit that a reviewer is not blocking the change.
• Changelog entries in the pull request title and/or Proposed changelog entries are accurate, human-readable, and in the imperative mood.
• Proper changelog labels are set so that the changelog can be generated automatically.
• If the change needs additional upgrade steps from users, the upgrade-guide-needed label is set and there is a Proposed upgrade guidelines section in the pull request title (see example).
• If it would make sense to backport the change to LTS, be a Bug or Improvement, and either the issue or pull request must be labeled as lts-candidate to be considered.

[Gautam-aman]

/label skip-changelog

[mawinter69]

Please make sure that you create a new branch based on the master/main and not from another branch that you already used for another change. This here is already part of #26099

[Gautam-aman]

@mawinter69 Thanks for the review.
I’ve opened a new PR with the same fix, rebased cleanly on master and without unrelated commits.
New PR: #26103
This PR can be closed in favor of the new one.