body { padding: 100px; background:#717171; }

#slider {

    width:400px;
    overflow:hidden;
    border: 10px solid #4C4C4C;
    height:266px;
    position:relative;
    margin:auto;
}

#slider ul {

    list-style-type: none;
    margin: 0;
    padding: 0;
    position: absolute;
    top: 0;
    left: 0;
    display: flex;

}


#slider ul li img {

    display: block;
	
}