SOURCE

<div class="yellow"> </div>

.yellow {
    position: relative;
    width: 12px;
    height: 12px;
    border-radius: 50%;
    background: #FFB22B;
    margin: 100px auto;
}

.yellow::after {
    content: '';
    position: absolute;
    top: 50%;
    left: 50%;
    transform: translate(-50%, -50%);
    width: 32px;
    height: 32px;
    background: #FFB22B;
    border-radius: 50%;
    opacity: 0.2;
    animation: breath 0.8s linear 0.5s infinite alternate;
}

@keyframes breath {
    0% {
        opacity: 0.2;
    }
    100% {
        opacity: 0;
    }
}