.test {
    width: 50%;
    height: 250px;
    background: linear-gradient(to right, rgba(255,255,255,1) 0%, rgba(255,255,255,0) 100%), linear-gradient(to bottom, green 0%, blue 100%);
    background-size: 100% 100%;

    animation: moving-gradient 1s infinite;
}

@keyframes moving-gradient {
    0% {
        background-position: left top;
    }

    100% {
        background-position: right bottom;
    }
}