script.js

  // (hours, minutes, seconds)
  let targetTime = new Date();
  targetTime.setHours(targetTime.getHours() + 4);
  targetTime.setMinutes(targetTime.getMinutes() + 6);
  targetTime.setSeconds(targetTime.getSeconds() + 3);

  let countdown = document.getElementById("countdown");

  setInterval(function () {
    let now = new Date();
    let diff = targetTime - now;

    let hours = Math.floor(diff / (1000 * 60 * 60));
    let minutes = Math.floor((diff / (1000 * 60)) % 60);
    let seconds = Math.floor((diff / 1000) % 60);

    countdown.innerText =
      "T-" +
      (hours < 10 ? "0" + hours : hours) + ":" +
      (minutes < 10 ? "0" + minutes : minutes) + ":" +
      (seconds < 10 ? "0" + seconds : seconds);

  }, 1000);