I think calling something "css-only" and having it break because you didn't add a radio input element in the markup is a little misleading. The dynamic function

I think calling something "css-only" and having it break because you didn't add a radio input element in the markup is a little misleading. The dynamic functionality hinges on the behavior of these html elements. And if having required html elements is ok, why not just lose the hacky markup and include a required javascript file to get the desired behavior in a more traditional and standard way?