[Shipping Labels Onboarding] Small improvements to the CTA scree

[hichamboushaba]

Part of: #6586

Description

This PR just adds two small improvements to the WCShip installation onboarding screen:

1. Make the CTA buttons sticky to the bottom of the screen, while the rest is scrollable.
2. Fix alignments of the bullet points in landscape.

Testing instructions

To access this new screen a site eligible for shipping labels is required for the #6620 to be displayed inside OrderDetail screen. Conditions for the banner to be shown:

• The store is located in US.
• The order currency is USD.
• The products are eligible for SL (not virtual/downloadable).
• The order is not eligible for IPP.
• WC Shipping plugin must be uninstalled or unactive

Once the banner is shown, click on "Get WooCommerce Shipping" button and the new screen should be displayed, please confirm that the above two changes are working as expected.

Images/gif

• I have considered if this change warrants user-facing release notes and have added them to RELEASE-NOTES.txt if necessary.

[peril-woocommerce]

You can trigger optional UI/connected tests for these changes by visiting CircleCI here.

[wpmobilebot]

You can test the changes on this Pull Request by downloading an installable build, or scanning this QR code:

[nbradbury]

Looks good!