/* main css */
#mydiv {
  width: 90vw;
  height: 80vh;
  margin: 0 auto;
  overflow: hidden;
  background-color: rgba(0,0,0,.5);
  width: 33vw
}
ul {
  overflow: hidden;
  position: relative;
  width: 600vw;
  top: 0;
  padding: 0;
  transition: all .5s;
}
li {
  text-align: center;
  display: inline-block;
  top: 0;
  position: relative;
  width: 33vw;
}
@media screen and (orientation: portrait) {
  #mydiv {
    width: 90vw;
  }
  li {
    width: 90vw;
  }
}
li img {
  max-width: 75%;
  margin: 0 12.5%;
}