Prototype Hide All elements of a class

Question

I can show/hide with IDs, however how do I do it with classes?

$('black').setStyle({
  display:'none', border:'1px solid red'
});

For example that will work if I had #black, but what if I have .black?

Thanks,

Answer 1

Got it!

$$('.black').each(
   function (e) {
      e.setStyle({border:'1px solid red'}); 
   } 
);