chore(components, styles): use px instead of rem for header styles

[alizedebray]

📄 Description

This PR replaces all rem values by px values in the header so it is easier to align with Figma.

---

🔮 Design review

• Design review done
• No design review needed

🧪 Visual regression tests

• Visual changes detected and approved (Check this box if VRT fails and changes are intentional)

📝 Checklist

• ✅ My code follows the style guidelines of this project
• 🛠️ I have performed a self-review of my own code
• 📄 I have made corresponding changes to the documentation
• ⚠️ My changes generate no new warnings or errors
• 🧪 I have added tests that prove my fix is effective or that my feature works
• ✔️ New and existing unit tests pass locally with my changes

[changeset-bot]

⚠️ No Changeset found

Latest commit: 6dcbccd

Merging this PR will not cause a version bump for any packages. If these changes should not result in a new version, you're good to go. If these changes should result in a version bump, you need to add a changeset.

This PR includes no changesets

When changesets are added to this PR, you'll see the packages that this PR includes changesets for and the associated semver types

Click here to learn what changesets are, and how to add one.

Click here if you're a maintainer who wants to add a changeset to this PR

[swisspost-bot]

Related Previews

• https://preview-8336--swisspost-design-system.netlify.app?devModeEnabled=true

[alionazherdetska]

Please revert changes to apps/documentation/src/stories/components/tabs/tabs.stories.ts.

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud