if(navigator.appName=="Netscape"){
  if(navigator.appVersion.indexOf("Mac")!=-1){
    document.write('<link rel="stylesheet" type="text/css" href="/top_css/style_mac.css" title="fontproperty">');
  } else if(navigator.appVersion.indexOf("Win")!=-1) {
    document.write('<link rel="stylesheet" type="text/css" href="/top_css/win_nn.css" title="fontproperty">');
  }
} else if(navigator.appName=="Microsoft Internet Explorer"){
  if(navigator.appVersion.indexOf("Mac")!=-1){
    document.write('<link rel="stylesheet" type="text/css" href="/top_css/style_mac.css" title="fontproperty">');
  } else if(navigator.appVersion.indexOf("Win")!=-1) {
    document.write('<link rel="stylesheet" type="text/css" href="/top_css/win_ie.css" title="fontproperty">');
  }
}