Homepage: Padding and spacing adjustments for Mainframe

[TasoOneAsia]

Proposed changes

Small collection of tweaks to adjust spacing and padding on the homepage.

• Also adjusts the sidebar to remove the unique styling for edge nodes as @danielledeleo had previously instructed

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/372/

---