Search A Specific Website With Quick Website Search
You can search a specific website using Safari's address field and Quick Website Search. Make sure this feature is enabled and then you can check the list of sites already added. You can add most other sites by performing a native search at that site. Once added, when you type the domain name of that site and a search term you then have the option to search that site directly instead of through a search engine. This works on Mac and iOS.