Review and update loading skeleton styles

[HaSistrunk]

Describe the bug

Loading skeletons do not always have the expected spacing or layout, specifically in the My List modals and on the Agent page. These are not captured in the visual regression testing, so we should comprehensively review all the loading styles.

To reproduce

Steps to reproduce the behavior:

1. Add items to your DIMES list
2. Go to the My List page
3. Open the Request Copies modal
4. See that the loading skeletons for possible error messages do not have a sufficient top margin

Expected behavior

A clear and concise description of what you expected to happen.

Error message or screenshots

My List modal:

Impact on your work

No major impact, but doesn't match the original design of DIMES and doesn't use loading skeletons to their full potential to allow users to anticipate exactly where content may appear when loading is complete.