.shadow {
    position:absolute;
    top:50%;
    left:50%;
    margin-top:-50px;
    margin-left:-50px;
}

.loader {
    background: -webkit-linear-gradient(left, skyblue 50%, #fafafa 50%); /* Foreground color, Background colour */
    border-radius: 100%;
    height: 100px; /* Height and width */
    width: 100px; /* Height and width */
    animation: time 8s steps(500, start) infinite;
}
.mask {
    border-radius: 100% 0 0 100% / 50% 0 0 50%;
    height: 100%;
    left: 0;
    position: absolute;
    top: 0;
    width: 50%;
    animation: mask 8s steps(250, start) infinite;
    transform-origin: 100% 50%;
}
@-webkit-keyframes time {
    100% {
        transform: rotate(360deg);
    }
}
@-webkit-keyframes mask {
    0% {
        background: #fafafa; /* Background colour */
        transform: rotate(0deg);
    }
    50% {
        background: #fafafa; /* Background colour */
        transform: rotate(-180deg);
    }
    50.01% {
        background: skyBlue; /* Foreground colour */
        transform: rotate(0deg);
    }
    100% {
        background: skyBlue; /* Foreground colour */
        transform: rotate(-180deg);
    }
}​