body {
    margin: 0;
    padding: 0;
    background: #313131;
}

.slider{
    width: 1300px;
    height: 500px;
    background: url(IMG-1.JPG) ;
    margin: 100px auto;
    animation: slide 20s infinite;
}

@keyframes slide {
    25%{
        background: url(IMG-4.JPG);
    }
    50%{
        background: url(IMG-3.jpg);
    }

    75%{
        background: url(IMG-2.jpg);
    }

    100%{
        background: url(IMG-1.JPG);
    }


}