Tweak admin redesign

[moorscode]

Summary

Three small tweaks needed to complete Yoast/wordpress-seo#15591

This PR can be summarized in the following changelog entry:

• N/A

Relevant technical choices:

• N/A

Test instructions

This PR can be tested by following these steps:

• Use this branch while checking out the branch of Tweak admin redesign wordpress-seo#15591 and follow instructions on that PR.

Impact check

• This PR affects the following parts of the plugin, which may require extra testing:
  • Only CSS changes

UI changes

• This PR changes the UI in the plugin. I have added the 'UI change' label to this PR.

Quality assurance

• I have tested this code to the best of my abilities
• I have added unittests to verify the code works as intended

Fixes #