Fix minor UI nits on campaigns
Created by: eseliger
I tried to make the review as simple as possible, so I've created atomic commits for the changes.
Closes https://github.com/sourcegraph/sourcegraph/issues/13210 Closes https://github.com/sourcegraph/sourcegraph/issues/13629
This PR is missing two things:
- Adding a background tint to the changeset
- Changing the global design of filters of the FilteredConnection component
Both are to be done, but I want to get this merged first, so we have these changes in the release for sure.