Can i retrieve an css attribute from a rule, in a LINK tag stylesheet ?

Can i retrieve an css attribute from a rule, in a LINK tag stylesheet ?

I don´t know if i am in the right way. I wish to extract some features of the "theme" link tag and them apply in other elements. For example, extract backgroundColor from rule .ui-widget-state-active, work in that color and them apply it in a color of other element.
In fact, i wish generate a style tag, completing theme stylesheet, but using some collors directly from the choosed theme.
Is it possible without tricks ?