So far, so good. You"ve found a web site. But the web site isn"t going to give you the coordinates.
To get the coordinates, your browser isn"t going to help.
There is no Geochecker, because it"s the kind of puzzle which, when you have solved it, you have no doubts at all that you have the right solution.
What you can have, however, is a hint that you can use after you have discovered the coordinates.
Behind the green box.