Refactor CSS margins and padding + CSS code cleanup

[lamATnginx]

Proposed changes

• Refactored usages of margin-X, where X is top, bottom, left, and right, to use margin-inline or margin-block wherever appropriate.
• Refactored usages of padding-X, where X is top, bottom, left, and right, to use padding-inline or padding-block wherever appropriate.
• Reordered CSS code to be more readable and logical.

Checklist

Before creating a PR, run through this checklist and mark each as complete.

• I have read the CONTRIBUTING document
• If applicable, I have added tests that prove my fix is effective or that my feature works
• If applicable, I have checked that any relevant tests pass after adding my changes
• I have updated any relevant documentation (README.md and CHANGELOG.md)

[github-actions]

✅ Deploy Preview will be available once build job completes!

Name	Link
😎 Deploy Preview	https://frontdoor-test-docs.nginx.com/previews/nginx-hugo-theme/317/

---