body {
  font-family: Arial, Helvetica, sans-serif;
  background: #f0f4f8;
  color: #333;
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: flex-start;
  min-height: 100vh;
  margin: 0;
  padding: 20px;
}

h1 {
  margin-bottom: 1rem;
}

.input-group {
  display: flex;
  gap: 0.5rem;
  align-items: center;
  margin-bottom: 1rem;
}

#seconds {
  width: 4rem;
  padding: 0.2rem;
}

#startBtn {
  padding: 0.3rem 0.6rem;
  cursor: pointer;
}

.countdown-display {
  font-size: 3rem;
  font-weight: bold;
  margin-top: 1rem;
}