テンプレート:テスト2/style.css

.grainbow {
  animation: grainbow .4s linear infinite normal;
  transition-duration: 1s;
}
@keyframes grainbow {
  0% {background: linear-gradient(90deg, red, orange, yellow, green, blue, purple)}
  20% {background: linear-gradient(90deg, orange, yellow, green, blue, purple, red)}
  40% {background: linear-gradient(90deg, yellow, green, blue, purple, red, orange)}
  60% {background: linear-gradient(90deg, green, blue, purple, red, orange, yellow)}
  80% {background: linear-gradient(90deg, blue, purple, red, orange, yellow, green)}
  100% {background: linear-gradient(90deg, purple, red, orange, yellow, green, blue)}
}