JSFiddle - React, Tailwind, and code Playground

HTML

<div id="clockbox">
    <div id="clockboxtext"></div>
</div>

CSS

#clockbox {
    border-width:1px;
    border-style:solid;
    border-color:red;
    padding:5px;
    width:210px;
    height:220px;
}
#clockboxtext {
    margin-top:50px;
    font-family:'Calibri';
    color:#CCCCCC;
    margin-left:5px;
}
#nday {
    font-size:35px;
}
#time {
    font-size:50px;
}
.ap {
    font-size:20px;
}
#date {
    font-size:30px;
}

JavaScript

tday = new Array("Sonntag", "Montag", "Dienstag", "Mittwoch", "Donnerstag", "Freitag", "Samstag");
tmonth = new Array("Januar", "Februar", "März", "April", "Mai", "Juni", "Juli", "August", "September", "Oktober", "November", "December");

function GetClock() {
    var d = new Date(+new Date + 12096e5);
    var test = new Date();
    var dx = d.toGMTString();
    dx = dx.substr(0, dx.length - 3);
    d.setTime(Date.parse(dx));
    d.setSeconds(d.getSeconds() + 0);
    var nday = d.getDay(),
        nmonth = d.getMonth(),
        ndate = d.getDate(),
        nyear = d.getYear(),
        nhour = test.getHours(),
        nmin = d.getMinutes(),
        nsec = d.getSeconds(),
        ap;

    /*     if(nhour===0){ap=" AM";nhour=12;}
else if(nhour<12){ap=" AM";}
else if(nhour==12){ap=" PM";}
else if(nhour>12){ap=" PM";nhour-=12;}*/

    if (nyear < 1000) nyear += 1900;
    if (nmin <= 9) nmin = "0" + nmin;
    if (nsec <= 9) nsec = "0" + nsec;

    var ndayUpper = tday[nday].toUpperCase();

    document.getElementById('clockboxtext').innerHTML = "<div id='nday'>" + ndayUpper + "</div><div id='time'> " + nhour + ":" + nmin + ":" + nsec + "</a></div><div id='date'>" + ndate + ". " + tmonth[nmonth] + " " + nyear + "</div>";
}

window.onload = function () {
    GetClock();
    setInterval(GetClock, 1000);
};