Rainbow CSS Gradient Background

HTML

<div id="rainbow"></div>

CSS

#rainbow {
    background: red; /* not working, let's see some red */
    background: -moz-linear-gradient( left ,
        rgba(255, 0, 0, 1) 0%,
        rgba(255, 255, 0, 1) 15%,
        rgba(0, 255, 0, 1) 30%,
        rgba(0, 255, 255, 1) 50%,
        rgba(0, 0, 255, 1) 65%,
        rgba(255, 0, 255, 1) 80%,
        rgba(255, 0, 0, 1) 100%);
    background: -webkit-gradient(linear,  left top,  right top, 
        color-stop(0%, rgba(255, 0, 0, 1)), 
        color-stop(15%, rgba(255, 255, 0, 1)),
        color-stop(30%, rgba(0, 255, 0, 1)),
        color-stop(50%, rgba(0, 255, 255, 1)),
        color-stop(65%, rgba(0, 0, 255, 1)),
        color-stop(80%, rgba(255, 0, 255, 1)),
        color-stop(100%, rgba(255, 0, 0, 1)));
}

#rainbow {
    width: 300px;
    height: 300px;
}