Update alternative background colour in dark theme

[bartaz]

Done

Updates dark theme alt background colour to #202020 to make it darker than default #262626.

Drive-by: top navigation items were updated to use hover theme colours instead of alt background.

QA

• Review affected examples, make sure they are using correct value.
• https://vanilla-framework-5128.demos.haus/docs/examples/patterns/strips/highlighted?theme=dark
  • highlighted strip in dark mode should be #202020 (background alt variable)

Check if PR is ready for release

If this PR contains Vanilla SCSS code changes, it should contain the following changes to make sure it's ready for the release:

• PR should have one of the following labels to automatically categorise it in release notes:
  • Feature 🎁, Breaking Change 💣, Bug 🐛, Documentation 📝, Maintenance 🔨.
• Vanilla version in package.json should be updated relative to the most recent release, following semver convention:
  • if CSS class names are not changed it can be bugfix relesase (x.x.X)
  • if CSS class names are changed/added/removed it should be minor version (x.X.0)
  • see the wiki for more details
• Any changes to component class names (new patterns, variants, removed or added features) should be listed on the what's new page.

Screenshots

[webteam-app]

Demo

Jenkins

demos.haus