* {
  box-sizing: border-box;
  margin: 0;
  padding: 0;
}

h1 {
  text-align: center;
  color: #d000ff;
  font-size: 50pt;
  -webkit-text-stroke: 2px blue;
}

body {
  font-family: system-ui, -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, Oxygen, Ubuntu, Cantarell, sans-serif;
  line-height: 1.5;
  min-height: 100vh;

  display: flex;
  justify-content: center; 
  align-items: center;    

  background-image: 
    url('https://media.tenor.com/qJRMLPlR3_8AAAAi/maxwell-cat.gif'), 
    linear-gradient(
      135deg,
      #ff0000,
      #ff7f00,
      #ffff00,
      #00ff00,
      #0000ff,
      #4b0082,
      #8f00ff,
      #ff0000,
      #ff7f00,
      #ffff00,
      #00ff00,
      #0000ff,
      #4b0082,
      #8f00ff,
      #ff0000
    );

  background-size: 20% auto, 200% 200%;
  background-repeat: repeat, repeat;

  animation: rainbowScroll 8s linear infinite;
}

@keyframes rainbowScroll {
  0% {
    background-position: 0 0, 100% 100%;
  }
  100% {
    background-position: 0 0, 0% 0%;
  }
}