CSS3 selector to find the 2nd div of the same class

<div class="foo">...</div>
<div class="bar">...</div>
<div class="baz">...</div>
<div class="bar">...</div>

// set style:
$$('div.theclassname')[1].setStyle({ backgroundColor: '#900', fontSize: '1.2em' });
// OR add class name:
$$('div.theclassname')[1].addClassName('secondclass'); // pun intentded...

.bar:nth-child(2)

.foo:nth-child(2)

<div>
 <div class="foo"></div>
 <div class="foo"Find me</div>
...

<div>
 <div class="other"></div>
 <div class="foo"></div>
 <div class="foo">Find me</div>
 ...

$('.foo:eq(1)').css('color', 'red');

<div>
  <div class="other"></div>
  <div class="foo"></div>
  <div class="foo">Find me</div>
  ...

<div class="foo"></div>
<div class="foo last"></div>

.foo {}
.foo.last {}