<div class="date" id="time"></div>

body {
  display: flex;
  height: 100vh;  
  align-items: center;
  justify-content: center;
 }

#time {
   position: relative;
   color: #333;
   font-size: 50px;
   font-family: Impact, Charcoal, sans-serif;
   letter-spacing: 10px;  
   text-align: center;
}

function getDateTime() {
        var now     = new Date(); 
        var year    = now.getFullYear();
        var month   = now.getMonth()+1; 
        var day     = now.getDate();
        var hour    = now.getHours();
        var minute  = now.getMinutes();
        var second  = now.getSeconds(); 
        if(month.toString().length == 1) {
             month = '0'+month;
        }
        if(day.toString().length == 1) {
             day = '0'+day;
        }   
        if(hour.toString().length == 1) {
             hour = '0'+hour;
        }
        if(minute.toString().length == 1) {
             minute = '0'+minute;
        }
        if(second.toString().length == 1) {
             second = '0'+second;
        }   
        var dateTime = year+'/'+month+'/'+day+' </br>'+hour+':'+minute+':'+second;   
         return dateTime;
    }

    setInterval(function(){
        currentTime = getDateTime();
        document.getElementById("time").innerHTML = currentTime;
    }, 1000);