Fix documentation issues

[Jeremy-Walton]

Why?

There are a few issues in the documentation site that were noticed. Additionally, some dependencies were out of date.

What Changed

• Fix dark mode bug on introduction page
• Update dependencies
• Set explicit node version

Quality Assurance

Add an X to all that apply like this: [X]
Cross out all that don't apply with ~~ ~~ around it like this

• 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?

Screenshots

Old documentation

New documentation