.slider
{
    width:100%;
    height:450px;
    margin:0;
    overflow:hidden;
}

.slider ul
{
    display:flex;
    padding:0;
    width:400%;
    
    animation: cambio 20s infinite alternate;
}

.slider li
{
    width:100%;
    list-style:none;
}

.slider img
{
    width:100%;
    height:100%;
}

@keyframes cambio
{
    0%{margin-left:0;}
    20%{margin-left:0;}

    25%{margin-left:-100%;}
    45%{margin-left:-100%;}

    50%{margin-left:-200%;}
    70%{margin-left:-200%;}

    75%{margin-left:-300%;}
    100%{margin-left:-300%;}

}