body {
  margin: 0;
  width: 100vw;
  height: 100vh;
  background-image: 
    linear-gradient(140deg, 
      #00f3ffA0, 
      #0028b960 40%, 
      #00f3ff60 60%, 
      #00f3ffA0), 
    url("https://magazine-cf.techacademy.jp/wp-content/uploads/2021/02/14012940/typing_on_laptop_712.jpg");
  background-repeat: no-repeat;
  background-position: 50%;
  animation: move 20s infinite both;
}

@keyframes move{
  0% {
    background-size:100% auto;
  }
  50% {
    background-size:140% auto;
  }
  100% {
    background-size:100% auto;
  }
}