.main{
    background-image: url(images/pexels-valiphotos-589802.jpg);
    animation:   change 10s infinite ease-in-out;
}
@keyframes change{
    0%
    {
        background-image: url(images/pexels-bru-no-1461027.jpg);
    }
    20%
    {
        background-image: url(images/pexels-saymon-sami-202123-725100.jpg);
    }
    40%
    {
        background-image: url(images/pexels-janventer-6477338.jpg);
    }
    60%
    {
        background-image: url(images/pexels-lucaspezeta-2423412.jpg);
    }
    80%
    {
        background-image: url(images/pexels-quang-nguyen-vinh-222549-14035695.jpg);
    }
    100%
    {
        background-image: url(images/pexels-valiphotos-589802.jpg);
    }
}