var osName = navigator.appVersion ;
var browser = navigator.appName ;
var winIEstylesheet = "css/style_winIE.css" ;
var winNNstylesheet = "css/style_winNN.css" ;
var macstylesheet = "css/style_mac.css" ;
    if(osName.indexOf('Mac')!=-1){
    document.write("<link rel=\"stylesheet\" href=\"" + macstylesheet + "\" type=\"text/css\">");
    }
      else if(osName.indexOf('Win')!=-1){
          if(browser.charAt(0)=='NN'){
　　　　　document.write("<link rel=\"stylesheet\" href=\"" + winNNstylesheet + "\" type=\"text/css\">");
          }
            else if(browser.charAt(0)=='M'){
　　　　　  document.write("<link rel=\"stylesheet\" href=\"" + winIEstylesheet + "\" type=\"text/css\">");
            }
    }