The search option in the new docs.oracle.com layout has been frustrating a lot of people. When you first try it out, it seems like many of the options that used to be there - like searching within a specific library - are gone.
The good news is that you can still narrow your search to a specific product category. When you do a search, you can select a product category on the left to narrow your search:
You can then click down below, where it says "6 products", to narrow your search to the Ops Center 12.2.1 library:
If you do a search from inside one of the books in a library, this is done automatically.