body {
    background: url('https://www.transparenttextures.com/patterns/black-linen.png');
    background-size: cover;
    position: relative;
    overflow-x: hidden;
  }
  
  header {
    padding: 60px 0;
  }
  
  .bubble {
    position: absolute;
    border-radius: 50%;
    opacity: 0.4;
    background: #fff;
    animation: float 10s infinite;
  }
  
  .bubble:nth-child(1) { width: 40px; height: 40px; left: 20%; animation-delay: 0s; }
  .bubble:nth-child(2) { width: 60px; height: 60px; left: 50%; animation-delay: 2s; }
  .bubble:nth-child(3) { width: 30px; height: 30px; left: 80%; animation-delay: 4s; }
  .bubble:nth-child(4) { width: 50px; height: 50px; left: 10%; animation-delay: 6s; }
  .bubble:nth-child(5) { width: 20px; height: 20px; left: 70%; animation-delay: 8s; }
  
  @keyframes float {
    0% { bottom: -100px; }
    100% { bottom: 100vh; }
  }
  
  footer {
    background-color: #333;
    color: white;
    padding: 20px;
    text-align: center;
    margin-top: 40px;
  }