Update carousel style since AMP 1.5.1

[thomasguillot]

All Submissions:

• Have you followed the Newspack Contributing guideline?
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Changes proposed in this Pull Request:

Since AMP 1.5.1 (or 1.5, I didn't check...) AMP removed a few css properties from AMP Carousel, including the left/right position of the prev/next buttons.

This PR adds some of these properties back. I also used em instead of px for placement to match the .entry-wrapper paddings.

I also restyled the bullet navigation to match the style in #382

How to test the changes in this Pull Request:

1. Downgrade AMP to 1.4.4
2. Add a Carousel block to a page
3. Notice the prev/next arrows -- there is a 16px gap
4. Upgrade AMP to latest version (currently 1.5.1)
5. Notice the gap -- it should be gone (error!)
6. Switch to this PR
7. Notice the gap -- it should be back (and has increased, from 16px to 1.5em)

Other information:

• Have you added an explanation of what your changes do and why you'd like us to include them?
• Have you written new tests for your changes, as applicable?
• Have you successfully ran tests with your changes locally?

[claudiulodro]

Looks good. I was able to reproduce the issue on AMP 1.5.3, and this solves it nicely. Good catch!

[matticbot]

🎉 This PR is included in version 1.3.0 🎉

The release is available on GitHub release

Your semantic-release bot 📦🚀