向倒计时添加进度条

<div id="progress-bar"></div>

#progress-bar {
  width: 100%;
  height: 10px;
  background-color: #f2f2f2;
}

#progress-bar .progress {
  height: 100%;
  background-color: #4caf50;
}

function startCountdown(duration) {
  var progressBar = document.getElementById("progress-bar");
  var progress = document.createElement("div");
  progress.className = "progress";
  progressBar.appendChild(progress);

  var interval = setInterval(function() {
    var width = (duration / 100) * 100;
    progress.style.width = width + "%";
    duration--;

    if (duration < 0) {
      clearInterval(interval);
      progressBar.removeChild(progress);
    }
  }, 1000);
}

startCountdown(60); // 倒计时60秒