Change style of all elements of a class via prototype javascript

Question

This is probably really simple, but the prototype docs on the $$(function) really suck. What do I DO with all the items once the function gives them to me?

First I tried:

$$('div.category').style.height = 400 +"px";

Then:

$$('div.category').each(.style.height = 400 +"px");

Finally:

for (x in $$('div.category'))
{
    x.style.height = 400 +"px";
}

None of them are working. Help?

Answer 1

$$('div.category').each(function(d){
    d.style.height = '400px';
});

Answer 2

$$('div.category').invoke('setStyle', { height: '400px' });

Read more on invoke.