Steps to reproduce:

1. Login to backoffice.
2. Go to Content / Content structure.
3. Create new content "Landing page".
4. Add random block to Landing page zone e.g. Forms
5. Go to block settings.
6. Switch between tabs.
7. Verify styles of tabs.

Actual result:

See attachment.

Selected block tabs are grayed out.

Expected result:

Block tabs are properly styled.