Element.setStyle sets the style of element.
Available in script.aculo.us V1.5
As of (prototype V1.4.0)
Element.setStyle(element, {cssProperty: value [, ...]});
<p id="myparagraph">This is just some random text.</p>
<p>
<a href="#" onclick="Element.setStyle('myparagraph', {textAlign:'right'} ); return false;">
align right
</a>
</p>
creates:
This is just some random text.