SOURCE

<div class="loading"></div>

.loading{
    margin: 100px auto;
    width: 30px;
    height: 30px;
    border-radius: 50%;
    animation: loading 2s linear infinite;
    /* background: red */
    background-color: transparent;
}

@keyframes loading{
     0% {
        box-shadow: -40px 0 0 rgba(250, 189, 189, 0),
                    inset 0 0 0 15px rgba(250, 189, 189, 0),
                    40px 0 0 rgba(250, 189, 189, 0);
    }
    30% {
        box-shadow: -40px 0 0 rgba(250, 189, 189, 1),
                    inset 0 0 0 15px rgba(250, 189, 189, 0),
                    40px 0 0 rgba(250, 189, 189, 0);
    }
    60% {
        box-shadow: -40px 0 0 rgba(250, 189, 189, 0),
                    inset 0 0 0 15px rgba(250, 189, 189, 1),
                    40px 0 0 rgba(250, 189, 189, 0);
    }
    100% {
        box-shadow: -40px 0 0 rgba(250, 189, 189, 0),
                    inset 0 0 0 15px rgba(250, 189, 189, 0),
                    40px 0 0 rgba(250, 189, 189, 1);
    }


}