[JS/CSS] Getting CSS Properties in HEAD of document

[Invent]

Hi,

I know how to use Javascript to get the value of a CSS Property of a DIV when the DIV uses a style attribute. (style="/* */")

BUT, how can I get CSS Properties that are declared in the HEAD of the document? (<style type="text/css"></style>).

I can get the style object by doing:
document.body.style

But how can I get say the CSS Properties of the class "buttons" using js?

Thanks if you can help!
-Simon