body {
  margin: 0;
}

body {
  animation: rainbow 1s linear infinite;
  height: 100vh;
  overflow: hidden;
}

body,
html {
  height: 100vh;
  width: 100vw;
}

img {
  position: absolute;
}

@keyframes rainbow {
  0%   { background-color: red; }
  14%  { background-color: orange; }
  28%  { background-color: yellow; }
  42%  { background-color: green; }
  57%  { background-color: blue; }
  71%  { background-color: indigo; }
  85%  { background-color: violet; }
  100% { background-color: red; }
}