Fix chevron top on mobile

[lemacarl]

Done

Set chevron top to 1rem on mobile and 1.25rem on desktop

Fixes #4758

QA

• Open demo
• Check chevron height in mobile and desktop mode using developer tools

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.

[webteam-app]

Demo:
https://vanilla-framework-4853.demos.haus/docs/examples/patterns/navigation/default-dark
https://vanilla-framework-4853.demos.haus/docs/examples/patterns/navigation/sliding-dark

[bartaz]

Works great, thank you for your contribution @lemacarl!