minor adjustments to theme colors

[janette]

fixes #2955

QA Steps

• Add manual QA steps in checklist format for a reviewer to perform to confirm that the feature or fix is working. Include as much details as possible so that the reviewer doesn't lose time figuring out how to perform steps.

Merge process

• Note if there is a special sequence for merging (such as PRs on other repos that need to be merged first) or other abnormalities to look out for.

Reminders

• There is test for the issue.
• Coding standards checked.
• Review docs.getdkan.com (or in /docs) to see if it still covers the scope of the PR and update if needed.

[erogray]

Blocked by https://github.com/NuCivic/dkan_management/issues/266