body {
    margin: 0;
    height: 100vh;
    display: flex;
    justify-content: center;
    align-items: center;
    font-family: 'Arial', sans-serif;
    background-color: #f0f0f0;
    color: #000;
    transition: background-color 0.3s, color 0.3s;
  }
  
  .countdown {
    text-align: center;
  }
  
  .countdown h1 {
    margin: 0;
    color: #000;
    font-size: calc(1rem + 5vw);
  }
  
  .countdown .timer {
    font-size: calc(2rem + 10vw);
    font-weight: bold;
    color: #000;
  }
  
  body.dark-mode {
    background-color: #333;
    color: #fff;
  }
  
  body.dark-mode .countdown h1,
  body.dark-mode .countdown .timer {
    color: #fff;
  }