.rainbow {
    width:  stretch;
    height: 3px;
    background: -webkit-linear-gradient(left, red,orange,yellow,green,blue,indigo,violet);
    background: -moz-linear-gradient(left, red,orange,yellow,green,blue,indigo,violet,red);
    background: -o-linear-gradient(left, red,orange,yellow,green,blue,indigo,violet,red);
   
    background: linear-gradient(to right, red,orange,yellow,green,blue,indigo,violet,red);
    background-repeat: repeat-x;
    -webkit-animation: go 5s linear infinite;
    -moz-animation: go 5s linear infinite;
    -o-animation: go 5s linear infinite;
    
    animation: go 5s linear infinite;
}

@-webkit-keyframes go {
    0% {
        background-position: 0;
    }

    100% {
        background-position: 3200px 0;
    }
}

@-moz-keyframes go {
    0% {
        background-position: 0;
    }

    50% {
        background-position: 3200px 0;
    }

    100% {
        background-position: 200px 0;
    }
}

@-o-keyframes go {
    0% {
        background-position: 0;
    }

    100% {
        background-position: 3200px 0;
    }
}

@-ms-keyframes go {
    0% {
        background-position: 0;
    }

    100% {
        background-position: 3200px 0;
    }
}

@keyframes go {
    0% {
        background-position: 0;
    }

    100% {
        background-position: 3200px 0;
    }
}