Google doesn’t offer a way to unearth custom search engines built by other users, but by using a regular Google search you can find those homepages effortlessly. You just have to add [site:google.com inurl:coop/cse] to your search query. For example, you can use [site:google.com inurl:coop/cse css] to find custom search engines for CSS.
This might be useful if you have to do some research on a narrow topic and the regular Google search doesn’t return good results. By restricting your search to a list of sites about CSS or web programming, you’ll definitely find great results even for ambiguous queries like “position” or “display” .
Google Operating system has created a custom search for finding custom search engines