.stars {
    margin: 0 auto;
    position: fixed;
    top: 0;
    z-index: 2;
}

.star, .r{
    display: block;
    width: 1px;
    background: transparent;
    position: absolute;
    opacity: 0;
    /*过渡动画*/
    animation: star-fall 3s linear;
}

.star:after, .r:after  {
    content: '';
    display: block;
    border: 0px solid #fff;
    border-width: 0px 90px 2px 90px;
    border-color: transparent transparent transparent rgba(255, 255, 255, .5);
    box-shadow: 0 0 1px 0 rgba(255, 255, 255, .1);
    /*变形*/
    transform: rotate(225deg) translate3d(1px, 3px, 0);
    transform-origin: 0% 100%;
}

@keyframes star-fall {
    0% {
        opacity: 0;
        transform: scale(0.5) translate3d(0, 0, 0);
    }

    50% {
        opacity: 1;
        transform: translate3d(200px, 200px, 0);
    }

    100% {
        opacity: 0;
        transform: scale(1.2) translate3d(300px, 300px, 0);
    }
}