Gib mal im Reiter Erweitert folgendes ein:

<style>

#Zeit {text-align:left;font-family:Arial;font color=#FFFF00;font-weight: bold;} 

</style>

Was meinst Du mit Reiter?

setInterval(function() {

    var timespan = countdown(new Date("01/01/2011"), new Date());

    var div = document.getElementById('Zeit');

    div.innerHTML = "geboren am 01.01.2011, vergangene Zeit bis heute: " + timespan.years + " Jahre, " + timespan.months + " Monate, " + timespan.days + " Tage."

}, 1000);
</script>
<div id="Zeit"></div>
Oben = Original

------------------------------------------------------------------------------------------------------------------------------  

setInterval(function() {

    var timespan = countdown(new Date("01/01/2011"), new Date());

    var div = document.getElementById('Zeit');

    div.innerHTML = "geboren am 01.01.2011, vergangene Zeit bis heute: " + timespan.years + " Jahre, " + timespan.months + " Monate, " + timespan.days + " Tage."

}, 1000);

<style>

#Zeit {text-align:left;font-family:Arial;font color=#FFFF00;font-weight: bold;} 

</style>

</script>
<div id="Zeit"></div>

Im HTML-Objekt gibt es den Reiter "Allgemein", da ist der Code drin. Und nebendran ist der Reiter "Erweitert". Da gehört der style-Definition rein. 

So wie Du es gemacht hast ist falsch. Wenn dann gehört die style-Definition außerhalb des script-Teils. 

Erweitert
CSS-Code

Ich hatte jetzt folgendes dort rein kopiert:

<style>

#Zeit {text-align:left;font-family:Arial;font color=#FFFF00;font-weight: bold;} 

</style>

Abe es verändert sich leider nichts.

Vielen Dank für Eure Tipps!

<script>varmodule,countdown=function(r){functionv(a,b){var c=a.getTime();a.setUTCMonth(a.getUTCMonth()+b);returnMath.round((a.getTime()-c)/864E5)}functiont(a){var b=a.getTime(),c=newDate(b);c.setUTCMonth(a.getUTCMonth()+1);returnMath.round((c.getTime()-b)/864E5)}functionf(a,b){return a+" "+(1===a?p[b]:q[b])}functionn(){}functionl(a,b,c,g,x,d){0<=a[c]&&(b+=a[c],delete a[c]);b/=x;if(1>=b+1)return0;if(0<=a[g]){a[g]=+(a[g]+b).toFixed(d);switch(g){case"seconds":if(60!==a.seconds||isNaN(a.minutes))break; a.minutes++;a.seconds=0;case"minutes":if(60!==a.minutes||isNaN(a.hours))break;a.hours++;a.minutes=0;case"hours":if(24!==a.hours||isNaN(a.days))break;a.days++;a.hours=0;case"days":if(7!==a.days||isNaN(a.weeks))break;a.weeks++;a.days=0;case"weeks":if(a.weeks!==t(a.refMonth)/7||isNaN(a.months))break;a.months++;a.weeks=0;case"months":if(12!==a.months||isNaN(a.years))break;a.years++;a.months=0;case"years":if(10!==a.years||isNaN(a.decades))break;a.decades++;a.years=0;case"decades":if(10!==a.decades|| isNaN(a.centuries))break;a.centuries++;a.decades=0;case"centuries":if(10!==a.centuries||isNaN(a.millennia))break;a.millennia++;a.centuries=0}return0}return b}functionw(a,b,c,g,d,k){a.start=b;a.end=c;a.units=g;a.value=c.getTime()-b.getTime();if(0>a.value){var f=c;c=b;b=f}a.refMonth=newDate(b.getFullYear(),b.getMonth(),15);try{a.millennia=0;a.centuries=0;a.decades=0;a.years=c.getUTCFullYear()-b.getUTCFullYear();a.months=c.getUTCMonth()-b.getUTCMonth();a.weeks=0;a.days=c.getUTCDate()-b.getUTCDate(); 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f=0<f?20>f?Math.round(f):20:0;"function"===typeof a?(k=a,a=null):a instanceofDate||(a=null!==a&&isFinite(a)?newDate(a):null);"function"===typeof b?(k=b,b=null):b instanceofDate||(b=null!==b&&isFinite(b)?newDate(b):null);if(!a&&!b)returnnew n;if(!k)return w(new n,a||newDate,b||newDate,c,d,f);var l=c&1?1E3/30:c&2?1E3:c&4?6E4:c&8?36E5:c&16?864E5:6048E5,h,e=function(){k(w(new n,a||newDate,b||newDate,c,d,f),h)};e();return h=setInterval(e,l)}var s=Math.ceil,m=Math.floor,p,q,u;n.prototype.toString= function(){var a=u(this),b=a.length;if(!b)return"";1<b&&(a[b-1]="and "+a[b-1]);return a.join(", ")};n.prototype.toHTML=function(a){a=a||"span";var b=u(this),c=b.length;if(!c)return"";for(var d=0;d<c;d++)b[d]="\x3c"+a+"\x3e"+b[d]+"\x3c/"+a+"\x3e";--c&&(b[c]="and "+b[c]);return b.join(", ")};u=function(a){var b=[],c=a.millennia;c&&b.push(f(c,10));(c=a.centuries)&&b.push(f(c,9));(c=a.decades)&&b.push(f(c,8));(c=a.years)&&b.push(f(c,7));(c=a.months)&&b.push(f(c,6));(c=a.weeks)&&b.push(f(c,5));(c=a.days)&& b.push(f(c,4));(c=a.hours)&&b.push(f(c,3));(c=a.minutes)&&b.push(f(c,2));(c=a.seconds)&&b.push(f(c,1));(c=a.milliseconds)&&b.push(f(c,0));return b};d.MILLISECONDS=1;d.SECONDS=2;d.MINUTES=4;d.HOURS=8;d.DAYS=16;d.WEEKS=32;d.MONTHS=64;d.YEARS=128;d.DECADES=256;d.CENTURIES=512;d.MILLENNIA=1024;d.DEFAULTS=222;d.ALL=2047;d.setLabels=function(a,b){a=a||[];a.split&&(a=a.split("|"));b=b||[];b.split&&(b=b.split("|"));for(var c=0;10>=c;c++)p[c]=a[c]||p[c],q[c]=b[c]||q[c]};(d.resetLabels=function(){p="millisecond second minute hour day week month year decade century millennium".split(" "); q="milliseconds seconds minutes hours days weeks months years decades centuries millennia".split(" ")})();r&&r.exports?r.exports=d:"function"===typeofwindow.define&&window.define.amd&&window.define("countdown",[],function(){return d});return d}(module); setInterval(function() { var timespan = countdown(newDate("08/22/1886"), newDate()); var div = document.getElementById('Zeit'); div.innerHTML = "Die vergangene Zeit vom 22.08.1886 bis heute sind " + timespan.years + " Jahre, " + timespan.months + " Monate, " + timespan.days + " Tage, " + timespan.hours + " Stunden, " + timespan.minutes + " Minuten, " + timespan.seconds + " Sekunden." }, 1000); </script><divid="Zeit"></div>

...!... ... Nein!  <style> -Tag in der Anwendung (Tab) CSS - Experte des gleichen Objekts:
#Zeit {text-align:left;color:yellow;font-size:24px;font-weight: bold;}

... Alternative, Das <style> -Tag kann in Schritt 3 | Experte | ▪Benutzerdefinierter Code | 3. Option:
<style> #Zeit { text-align:left;color:yellow;font-size:24px;font-weight: bold;} </style>

.