fix(skip-link): give the skip link a more modern styling

[lorumic]

Done

• Updated style for the "skip link" pattern - see comparison screenshots below.

Fixes #5356

QA

• Open demo for the skip link pattern
• Click inside the iframe of the example, then press SHIFT + TAB to make the skip link appear
• Check the new appearance of the skip link

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 release (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

Before:

After:

[webteam-app]

Demo

Jenkins

demos.haus

[lyubomir-popov]

LGTM

[bartaz]

Looks good, thanks @lorumic !