@keyframes slider{
    0%{
        left: 0;
    }

    33.333333%{
        left: 0;
    }
    40%{
       left: -100%; 
    }
    73.333333%{
        left: -100%;
    }
    
    100%{
        left: -200%;
    }

}

#slider{
    overflow: hidden;
}
#slider figure iframe{

    width: 33.33333%;
    height: 100vh;;
    float: left;
}

#slider figure{
    position: relative;
    width: 300%;
    
    margin: 0;
    left: 0;
    animation: 30s slider infinite;

}