/customers style fixes

[mike-j-thomas]

Goal

Fix up these styling bugs

• Persistent dropshadow on case study cards. The dropshadow should only appear on hover
• Testimonials cards are missing the dropshadow on hover
• Top padding issue on featured case study slides on mobile
  • I assume this is caused by the differing height of content across slides. If it is unavoidable or a non-trivial fix, can we at least have the slides aligned top, so that the extra space is at the bottom, under the "Read their story" link?

Expected behavior:

Actual behavior:

[github-actions]

This issue has been automatically tagged as unreleased. If this is is incorrect, you may replace the label with ~released-bug. If this is correct, or might be correct, move this bug onto the appropriate product board to get a fix underway.