const startButton = document.querySelector("button");
startButton.onclick = function countdown() {
let sixtySeconds = 60;
let sixtyMinutes = 0;
document.querySelectorAll("span")[0].innerHTML = "0" +sixtyMinutes;
let timer = setInterval( function theTimer(){
  sixtySeconds--;
  if (sixtySeconds >= 10){
    document.querySelectorAll("span")[1].innerHTML = sixtySeconds;
  } else if (sixtySeconds < 10){
    document.querySelectorAll("span")[1].innerHTML = "0" + sixtySeconds;
  } else {
     document.querySelectorAll("span")[1].innerHTML = "00";
  }
  if (sixtySeconds === 0 || sixtyminutes < 60){
    sixtyMinutes++;
    document.querySelectorAll("span")[0].innerHTML = "0" +sixtyMinutes;
   clearInterval(timer);
  }
}, 1000);
 return countdown();
}