body {
    margin: 0;
    padding: 0;
    background: #000000;
}

.center {
    position: absolute;
    top: 50%;
    left: 50%;
    transform: translate(-50%, -50%);
}

.slider {
    background: url(https://2.bp.blogspot.com/-ZOQEZzLsB50/V89wZ4z27uI/AAAAAAAAAaU/UqejOE-PfQoVAGWO-gq3l__fPPQM9l7zgCLcB/s1920/Nature_Wave_Ocean_Sunset_Sunlight_Water_hd.jpg);
    background-size: cover;
    height: 450px;
    width: 800px;
    border-radius: 10px;
    box-shadow: 0px 5px 8px rgba(0, 0, 0, .3);
    animation: animate 10s infinite;
}

@keyframes animate {
    20% {
        background: url(https://wallpapers.com/images/hd/full-hd-background-0gn92jw6dpzfgcn8.jpg);
        background-size: cover;
    }
     40% {
        background: url(https://images4.alphacoders.com/568/thumb-1920-568792.jpg);
        background-size: cover;
    }
     60% {
        background: url(https://wallpaperaccess.com/full/140526.jpg);
        background-size: cover;
    }
     80% {
        background: url(https://wallpapers.com/images/hd/full-hd-background-0gn92jw6dpzfgcn8.jpg);
        background-size: cover;
    }
}