body {
    height: 100vh;
    width: 100vw;
    color: red;
    margin: 0;
    padding: 0;
  }
  
  div {
    position: absolute;
    top: 0;
    left: 0;
    background-size: cover;
    width: 100vw;
    height: 100vh;
  }
  
  .back {
    background-image: url('https://images.unsplash.com/photo-1666878093953-18a02f217e9a?ixlib=rb-4.0.3&ixid=MnwxMjA3fDB8MHxwaG90by1wYWdlfHx8fGVufDB8fHx8&auto=format&fit=crop&w=2070&q=80');
  }
  
  canvas {
    position: absolute;
    top: 0;
    left: 0;
    mix-blend-mode: multiply;
    height: 100vh;
    width: 100vw;
  }