<body dir="rtl"> is more appropriate as per W3C recommendation:
http://www.w3.org/International/questions/qa-bidi-css-markup
Because directionality is an integral part of the document structure, markup should be used to set the directionality for a document or chunk of information, or to identify places in the text where the Unicode bidirectional algorithm alone is insufficient to achieve desired directionality. […] You should therefore use dedicated bidi markup whenever it is available. Do not simply attach CSS styling to a general element to achieve the effect.
User-agents that ignore CSS will also benefit from this approach.