if ( navigator.appVersion.indexOf ( 'Win' ) != -1 ) { var archos = 'Win'; }
else if ( navigator.appVersion.indexOf ( 'Mac' ) != -1 ) { var archos = 'Mac'; }

document.open ( );
if ( archos == 'Win' ) {
document.writeln ( '<link rel="stylesheet" href="css/win.css" type="text/css">' );
} else if ( archos == 'Mac' ) {
document.writeln ( '<link rel="stylesheet" href="css/mac.css" type="text/css">' );
}
document.close ( );