windows and macintosh show differently a page

I have the following http://jsbin.com/ojeja4/2/edit

The button and the expiration date working correct in windows, in all browsers but in OS X in safari & firefox (and maybe others) I find out that the button and the expiration date isn't correct.

Below I have print screens:

Windows - Firefox and all other browsers

OS X - Firefox

OS X - Safari versions 3,4,5

I really can't understand what is the problem. I tried use position instead of margin and padding but the result still the same. I found a jquery script and I used it, which recognize the os and browser, but I don't see the reason for a css problem to use a jquery script. Is it a common problem between windows and os x or I did a mistake in code that I can't un开发者_高级运维derstand?

Thanks

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It could be because of the font. Your are using Arial on Windows and Helvetica on Mac. Try using a cross operating system font. Or maybe something like Google Font API.