@property --color-position {
  syntax: '<length-percentage>';
  inherits: false;
  initial-value: 30%;
}
body {
  margin: 0;
  overflow: hidden;
  --color-position: 30%;
  background: radial-gradient(circle at center, #F9F871, #FFD45A var(--color-position));
  animation: beat 3s infinite ease-in-out;
}
@keyframes beat {
  33%, 66% {
    --color-position: 160%;
  }
}