5.css

* {
    animation-name: changing;
    animation-duration: 12s;
    animation-iteration-count: infinite;
    
}

@keyframes changing {
    0%{
        background-image: url(assets/img1.jpg);
    }
    40%{
        background-image: url(assets/img2.jpg);
        
    }
    
    75%{
        background-image: url(assets/img3.jpg);
        
    }
    100%{
        background-image: url(assets/img1.jpg);
    }
}