.loader {
    position: relative;
    display: flex;
    align-items: center;
    justify-content: center;
    width: 100%;
    max-width: 3rem;
}
.loader:before,
.loader:after {
    content: "";
    position: absolute;
    border-radius: 50%;
    animation: pulsOut 1.8s ease-in-out infinite;
    filter: drop-shadow(0 0 0.5rem rgba(255, 255, 255, 0.75));
}
.loader:before {
    width: 100%;
    padding-bottom: 100%;
    box-shadow: inset 0 0 0 0.5rem #fff;
    animation-name: pulsIn;
}
.loader:after {
    width: calc(100% - 1rem);
    padding-bottom: calc(100% - 1rem);
    box-shadow: 0 0 0 0 #3b3b3b;
}

@keyframes pulsIn {
    0% {
        box-shadow: inset 0 0 0 0.5rem #3b3b3b;
        opacity: 1;
    }
    50%,
    100% {
        box-shadow: inset 0 0 0 0 #3b3b3b;
        opacity: 0;
    }
}

@keyframes pulsOut {
    0%,
    50% {
        box-shadow: 0 0 0 0 #3b3b3b;
        opacity: 0;
    }
    100% {
        box-shadow: 0 0 0 0.5rem #3b3b3b;
        opacity: 1;
    }
}