var OPER=navigator.userAgent.toLowerCase().indexOf("opera");
       var IE=navigator.appName.toLowerCase().indexOf("explorer");
       var b_version=navigator.appVersion;
       var version=parseFloat(b_version);
       var is = new Is();



       if(((OPER>-1)) && (version>=8))
       {   // Opera
         document.write("<link rel='stylesheet' href='"+percorso+"css/b_Opera.css' type='text/css'>");
       }
        else if ((IE>-1) && (version==4) && (is.ie7==0) && (is.ie6))
        { // Explorer - la versione 4.0 coincide con la versione 5.0 e 6.0 - confrontare  www.w3schools.com/js/js_browser.asp
            document.write("<link rel='stylesheet' href='"+percorso+"css/b_IE.css' type='text/css'>");
        }

        else
        { // resto dei browser conformi allo standard w3c: vedi Firefox 1.x
            document.write("<link rel='stylesheet' href='"+percorso+"css/b_Firefox.css' type='text/css'>");
        }
      // sezione - chiusura - carica i fogli di stile relativo ai browser




function Is() {
agent = navigator.userAgent.toLowerCase();
this.major = parseInt(navigator.appVersion);
this.minor = parseFloat(navigator.appVersion);
this.ns = ((agent.indexOf('mozilla') != -1) && ((agent.indexOf('spoofer') == -1) && (agent.indexOf('compatible') == -1)));
this.ns4 = (this.ns && (this.major == 4));
this.ns6 = (this.ns && (this.major >= 5));
this.ie = (agent.indexOf("msie") != -1);
this.ie3 = (this.ie && (this.major < 4));
this.ie4 = (this.ie && (this.major == 4) && (agent.indexOf("msie 5.0") == -1));
this.ie5 = (this.ie && (this.major == 4) && (agent.indexOf("msie 5.0") != -1));
this.ie55 = (this.ie && (this.major == 4) && (agent.indexOf("msie 5.5") != -1));
this.ie6 = (this.ie && (agent.indexOf("msie 6.0")!=-1) );
this.ie7 = (this.ie && (agent.indexOf("msie 7.0")!=-1) );
}