.signal {
    position: fixed;
    top: 45vh;
    left: calc(50% - 25px);
    border-width: 8px;
    border-style: solid;
    border-radius: 100%;
    height: 50px;
    width: 50px;
    opacity: 0;
    position: absolute;
    animation: pulsate .85s ease-out;
    animation-iteration-count: infinite;
}

@keyframes pulsate {
    0% {
        transform: scale(.1);
        opacity: 0.0;
    }

    50% {
        opacity: 1;
    }

    100% {
        transform: scale(1.2);
        opacity: 0;
    }
}
