* {
  margin: 0;
  padding: 0;
}

li {
  list-style: none
}

li {
  margin-right: 100px;
  margin-left:100px;
  height: 500px;
  border: 1px solid #ddd;
  font-size: 30px;
  text-align: center;
}

div {
  position: fixed;
  top: 50%;
  left:10px;
  margin-top:-120px;

}

div p {
  width: 60px;
  height: 30px;
  background: #ccc;
  border-top: 1px solid #fff;
  text-align: center;
  line-height: 30px;
  cursor: pointer;
}

div p.on {
  background: #666;
  color:#fff;
}