Sidebar and dialog improvements

[Jeremy-Walton]

Task

Fixes #302

Why?

The sidebar, navbar, and modal with dialog were a bit outdated and needed some improvement.

What Changed

• Add new token for setting the modal transition time
• Ensure navbar has a top border when used in the footer
• Ensure sidebar has a left border when used on the right side
• Update modal when used on <dialog> to greatly simplify and work better

Quality Assurance

• Have you tagged the PR with the correct labels?
• Have you validated the changes?
  • Have you run linters? (yarn sanity-check)
  • Have you run prettier?
  • Have you tried building the css?
  • Have you tried building storybook?
• Have you updated any usage of changed tokens?
• [ ] Did you add a component?
  • [ ] Have you added it to the dependency graph?
  • [ ] Have you added it to the docs?
• Did you update a component?
  • [ ] Have you updated the dependency graph?
  • Have you updated the docs?
• [ ] Do you need to update the package version?
  Planning on including in release v2.3.0

Screenshots