.loader {
    display: flex;
    flex-direction: row;
}

.loader div {
    position: relative;
    width: 36px;
    height: 200px;
    margin: 20px;
    overflow: hidden;
    border-radius: 40px;
    border: 2px solid rgba(0,0,0, 0.4);
    background: linear-gradient(to bottom, rgba(0, 0, 0, 0.05, #3b3b3b));
    box-shadow: 15px 15px 20px rgba(0, 0, 0, 0.1), -15px -15px 20px rgba(0,0,0, 0.4),
    inset -5px -5px 5px rgba(0, 0, 0, 0.1),
    inset 5px 5px 5px rgba(0, 0, 0, 0.1);
}

.loader div::before {
    content: " ";
    position: absolute;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
    z-index: 10;
    border-radius: 20px;
    box-shadow: 15px 15px 20px rgba(0, 0, 0, 0.1), -15px -15px 20px black,
    inset -5px -5px 5px rgba(0, 0, 0, 0.5),
    inset 5px 5px 5px rgba(0, 0, 0, 0.05);
}

.loader div::after {
    content: "";
    position: absolute;
    top: 0;
    left: 0;
    width: 36px;
    height: 36px;
    background: #fff;
    border-radius: 50%;
    box-shadow: inset -5px -5px 5px rgba(0, 0, 0, 0.2), 0 420px 0 400px #2196f3;
    animation: animate 2.5s ease-in-out infinite;
    transform: translateY(160px);
    animation-delay: calc(-0.5s * var(--i));
}

@keyframes animate {
    0% {
        transform: translateY(160px);
        filter: hue-rotate(180deg);
    }
    50% {
        transform: translateY(0px);
    }
    100% {
        transform: translateY(160px);
        filter: hue-rotate(0deg);
    }
}