svg {
    height: 100vh;
  }

  .layer {
    fill: #4b4b4b;  
    animation: 4s linear infinite;
  }
  
  .layer1 {
    animation-name: layer1;
  }
  
  .layer2 {
    animation-name: layer2;
  }
  
  .layer3 {
    animation-name: layer3;
  }  

  @keyframes layer1 {
    0%, 65% {
      fill: #b2b2b2;
    }
    75%, 82% {
      fill: #4b4b4b;
    }
    92%, 100% {
      fill: #b2b2b2;
    }
  }
  
  @keyframes layer2 {
    0%, 40% {
      fill: #b2b2b2;
    }
    50%, 86% {
      fill: #4b4b4b;
    }
    96%, 100% {
      fill: #b2b2b2;
    }
  }
  
  @keyframes layer3 {
    0%, 15% {
      fill: #b2b2b2;
    }
    25%, 90% {
      fill: #4b4b4b;
    }
    100% {
      fill: #b2b2b2;
    }
  }