Animate height using CSS transition http://jsfiddle.net/thechrisjordan/3Fc7D/23/ http://stackoverflow.com/questions/3508605/css-transition-height-0-to-height-auto

style.css

#selector {
    max-height: 0;
    transition: max-height 0.15s ease-out;
    overflow: hidden;
}

#selector.active {
    max-height: 500px;
    transition: max-height 0.25s ease-in;
}