Template:AnimatedRainbowText/rainbow.css

@keyframes rainbow{
   0%{color: red;}
   16%{color: orange;}
   32%{color: yellow;}
   48%{color: lime;}
   64%{color: cyan;}
   80%{color: blue;}
   90%{color: #FF00FF;}
   100%{color: red;}
}

.rainbow {
        animation: 2s rainbow
infinite;
}