Google doesn't provide a way to find custom search engines built by other users, but you can restrict a normal Google search to the homepages of those search engines. You just have to add [site:google.com inurl:coop/cse] to your 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".
To make things even easier, I created a custom search engine that searches through more than 100,000 custom search engines.
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