how can i change attribute of all css classes?

say i have a bunch of divs of a particular class. i want to click a button and change an attribute of that class for all the div instances. how could i do that with javascript?

.myCoolDiv{
background-color:red;
}
.
.
.
<div class="myCoolDiv">blah</div>
<div class="myCoolDiv">more blah</div>
< button to change all "myCoolDiv" backgrounds to "blue">

www.alistapart.com/index.html has a feature on their page where you can alter the display font with a button click. Check out their code for ideas.


wdn2k

they grab all the tags using getElementByTag and just switch out the style sheets. not quite what i was looking for, but might work