Throbbing Things in CSS

.throb {
    border: 3px solid #555;
    height: 50px;
    width: 50px;
    -webkit-border-radius: 50%;
    -webkit-animation: pulsate 2s ease-out;
    -webkit-animation-iteration-count: infinite;
    opacity: 0;
    z-index: 999;
}


@-webkit-keyframes pulsate {
    0% {
        -webkit-transform: scale(1.0, 1.0); opacity: 1.0;
    }
    50% {
        -webkit-transform: scale(0.75, 0.75); opacity: 0.5;
    }
    100% {
        -webkit-transform: scale(1.0, 1.0); opacity: 1.0;
    }
}