Neither Pages '09 or Pages v5.6.2 are HTML/CSS aware, as is MS Word, or LibreOffice Writer. Neither version of Pages is receiving the HTML/CSS directly. Safari translates the HTML/CSS to RTF, and then shoves that on the clipboard. When you paste, Pages attempts to translate the RTF code back into the attributed text that it understands.
Because Apple ripped RTF support out of Pages v5, you will more than likely need to paste from Safari into TextEdit (which does understand RTF natively), and then from there into Pages. Or you grab a screen shot of the browser content, and either drop it as an image into Pages, or use Preview to convert the screen shot into PDF, and then drop that into Pages.
All told, the ability to get what you see in a browser into Pages is daunting.