@keyframes hop {
  0% {
    background-image:
    radial-gradient(circle at calc(50% - 12vmin) calc(50% - 12vmin), blue 3vmin, #0000 0),
    radial-gradient(circle at calc(50% + 12vmin) calc(50% + 12vmin), blue 3vmin, #0000 0);
  }
  100% {
    background-image:
    radial-gradient(circle at calc(50% - 12vmin) calc(50% + 12vmin), blue 3vmin, #0000 0),
    radial-gradient(circle at calc(50% + 12vmin) calc(50% - 12vmin), blue 3vmin, #0000 0);
  }
}

:root {
  background:
    radial-gradient(circle at calc(50% - 12vmin) calc(50% - 12vmin), blue 4vmin, #0000 0),
    radial-gradient(circle at calc(50% + 12vmin) calc(50% + 12vmin), blue 4vmin, #0000 0);
  background-color: #ccc;
  min-height: 100vh;
  padding: 0;
  overflow: hidden;
  animation: hop 1.25s linear infinite;
}