<div class="button">
    <span>立即下载</span>
</div>

.button {
    width: 200px;
    height: 46px;
    line-height: 46px;
    background-color: #2e82ff;
    color: #ffffff;
    font-size: 18px;
    text-align: center;
    border-radius: 27px;
    position: relative;
}
.button::before {
    content: "";
    position: absolute;
    left: 0px;
    width: 100%;
    height: 100%;
    background-image: 
        linear-gradient(to right, rgba(255, 255, 255, 0) 30%, rgba(255, 255, 255, 0.2) 50%, rgba(255, 255, 255, 0) 70%);
    background-size: 200%;
    animation: wipes 1s infinite;
}
@keyframes wipes {
    0% {
        background-position: 0 0;
    }
    100% {
        background-position: 100% 0;
    }
}