Verification of jwt signed with base64 encoded secret fails on jwt.io

When I put a string YWFhYWFhYWFhYWFhYWFhYWFhYWFhYWFhYWFhYWFhYWE= (base64 for "aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa") as a secret with unchecked checkbox, it will produce same result as I get from java library.