Given
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The highest precedence goes to inline styles. style rules from external stylesheets follow a simple formula (see http://www.htmldog.com/guides/cssadvanced/specificity/)
as to the order of sheets, the rules in the last sheet would take precedence in the event of a collision (unless you use the !important flag)
edit: better ref on specificity http://css-tricks.com/specifics-on-css-specificity/