.stopwatch {
  font-family: system-ui, "Segoe UI", Roboto, Helvetica, Arial, sans-serif, "Apple Color Emoji", "Segoe UI Emoji", "Segoe UI Symbol";
  background: #1f2937;
  padding: 30px;
  border-radius: 20px;
  text-align: center;
  width: 300px;
  margin: 0 auto;
  box-shadow: 0 10px 30px rgba(0,0,0,0.2);
}
.time-display {
  font-size: 3.5rem;
  font-weight: 700;
  color: #fff;
  font-variant-numeric: tabular-nums;
  margin-bottom: 20px;
  text-shadow: 0 0 10px rgba(255,255,255,0.1);
}
.controls {
  display: flex;
  gap: 10px;
  justify-content: center;
}
.btn {
  padding: 10px 20px;
  border: none;
  border-radius: 8px;
  font-weight: 600;
  cursor: pointer;
  transition: transform 0.1s, opacity 0.2s;
  font-size: 1rem;
}
.btn:active {
  transform: scale(0.95);
}
.start {
  background: #10b981;
  color: white;
}
.stop {
  background: #ef4444;
  color: white;
}
.reset {
  background: #4b5563;
  color: white;
}

let [seconds, minutes, hours] = [0, 0, 0];
let display = document.getElementById("display");
let timer = null;

function stopwatch() {
  seconds++;
  if (seconds == 60) {
    seconds = 0;
    minutes++;
    if (minutes == 60) {
      minutes = 0;
      hours++;
    }
  }

  let h = hours < 10 ? "0" + hours : hours;
  let m = minutes < 10 ? "0" + minutes : minutes;
  let s = seconds < 10 ? "0" + seconds : seconds;

  display.innerHTML = h + ":" + m + ":" + s;
}

function startTimer() {
  if (timer !== null) {
    clearInterval(timer);
  }
  timer = setInterval(stopwatch, 1000);
}

function stopTimer() {
  clearInterval(timer);
}

function resetTimer() {
  clearInterval(timer);
  [seconds, minutes, hours] = [0, 0, 0];
  display.innerHTML = "00:00:00";
}

document.getElementById("startBtn").addEventListener("click", startTimer);
document.getElementById("stopBtn").addEventListener("click", stopTimer);
document.getElementById("resetBtn").addEventListener("click", resetTimer);