.banner{width:95%;margin:auto;overflow:hidden;}
.banner ul{display:flex;padding:0px;width:400%;animation:slide 20s infinite alternate;animation-timing-function:ease-out;}
.banner:nth-child(2) ul{animation-timing-function:step-start;}
.banner ul li{width:100%;list-style:none;}
.banner ul li img{width:100%;}

@keyframes slide{0%{margin-left:0;}33%{margin-left:0;}35%{margin-left:-100%;}68%{margin-left:-100%;}70%{margin-left:-200%;}100%{margin-left:-200%;}}