JSFiddle - React, Tailwind, and code Playground

HTML

<html>

<body>
  <div>Time left = <span id="timer"></span></div>

</body>

</html>

CSS

body{
  background-color:#2D3047;
}

div{
  background-color:#419D78;
  color:#EFD0CA;
  font-size:20px;
  text-align:center;
}

JavaScript

document.getElementById('timer').innerHTML =
  090+ ":" + 00;
startTimer();

function startTimer() {
  var presentTime = document.getElementById('timer').innerHTML;
  var timeArray = presentTime.split(/[:]+/);
  var m = timeArray[0];
  var s = checkSecond((timeArray[1] - 1));
  if(s==59){m=m-1}
  //if(m<0){alert('timer completed')}
  
  document.getElementById('timer').innerHTML =
    m + ":" + s;
  setTimeout(startTimer, 1000);
}

function checkSecond(sec) {
  if (sec < 10 && sec >= 0) {sec = "0" + sec}; // add zero in front of numbers < 10
  if (sec < 0) {sec = "59"};
  return sec;
}