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MacEdition Guide to CSS2 Support in Mac-only Browsers
Abridged Support of CSS-2
[last modified feb 15, 2003]
other browser and OS support is available at the top of the pages before the charts.
A List Apart did an article, but dated... On Mac Browsers and CSS [though you may find some of your answers in this piece, since MS has not upgraded the IE Mac version browser much, and those items may still be existing.]
MAC Browser Roundup - interviews with Tantek Çelik and Håkon Lie by Jeffrey Zeldman.
As far as Mac and CSS support goes, it has near total support for CSS - 1 items , somewhere about 99.0%, but CSS-2 I am not fully aware.
I know I have made some absolute positioned pages that work or display well on a Mac OSX, but I would have to check which ones. I did use the CascadeDTP tool[free for windows] to lay these pages out, and followed XHTML guidelines and DTD... though I do believe there is a free absolute positioning tool available for Moz users, and I am not sure what it is called, and I would guess it is workable on a Mac.
As far as space at edges/borders go... browsers have a different way of looking at this, and may have this visible padding that is only removed by use of a negative margin.
Another possible read.
Flexible layouts with CSS positioning -