<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
</head>
<body>
  <div class="timer"></div>
</body>
</html>
 body{
      display: flex;
      align-items: center;
      justify-content: center;
      height: 100vh;
      background-image: url("https://images.unsplash.com/photo-1553095066-5014bc7b7f2d?ixlib=rb-1.2.1&ixid=MnwxMjA3fDB8MHxzZWFyY2h8MXx8d2FsbCUyMGJhY2tncm91bmR8ZW58MHx8MHx8&w=1000&q=80");
      background-repeat: no-repeat;
      background-size: cover;
    }
    .timer{
    color: white;
font-size:56px;
font-weight: bolder;
border:5px solid white;
padding:50px;
border-radius:50%;
    }
var time=document.getElementsByClassName("timer")
 
 var timings=30;
 var i=0;
     var myInterval = setInterval(Timeout, 1000);
    function Timeout(){
      if((timings*60-i)%60>=10){
        time[0].innerHTML=parseInt(`${(timings*60-i)/60}`)+":"+`${(timings*60-i)%60}`;
      }
      else{
        time[0].innerHTML=parseInt(`${(timings*60-i)/60}`)+":0"+`${(timings*60-i)%60}`;
      }
      
     
      
i++;
    }

External CSS

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External JavaScript

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